Replace '_safelyVisitChild' with 'target?.accept()' in AST visiting.

pkg/analyzer/lib/src/dart/ast/ast.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.src.dart.ast.ast;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
@@ skipping 137 matching lines @@
         ..addAll(_metadata);
     } else {
       result.addAll(sortedCommentAndAnnotations);
     }
     return result;
   }
 
   @override
   void visitChildren(AstVisitor visitor) {
     if (_commentIsBeforeAnnotations()) {
-      _safelyVisitChild(_comment, visitor);
+      _comment?.accept(visitor);
       _metadata.accept(visitor);
     } else {
       for (AstNode child in sortedCommentAndAnnotations) {
         child.accept(visitor);
       }
     }
   }
 
   /**
    * Return `true` if there are no annotations before the comment. Note that a
@@ skipping 133 matching lines @@
   @override
   void set name(Identifier name) {
     _name = _becomeParentOf(name);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitAnnotation(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_name, visitor);
-    _safelyVisitChild(_constructorName, visitor);
-    _safelyVisitChild(_arguments, visitor);
+    _name?.accept(visitor);
+    _constructorName?.accept(visitor);
+    _arguments?.accept(visitor);
   }
 }
 
 /**
  * A list of arguments in the invocation of an executable element (that is, a
  * function, method, or constructor).
  *
  *    argumentList ::=
  *        '(' arguments? ')'
  *
@@ skipping 203 matching lines @@
   @override
   void set type(TypeName name) {
     _type = _becomeParentOf(name);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitAsExpression(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_expression, visitor);
-    _safelyVisitChild(_type, visitor);
+    _expression?.accept(visitor);
+    _type?.accept(visitor);
   }
 }
 
 /**
  * An assert statement.
  *
  *    assertStatement ::=
  *        'assert' '(' [Expression] ')' ';'
  */
 class AssertStatementImpl extends StatementImpl implements AssertStatement {
@@ skipping 83 matching lines @@
   @override
   void set message(Expression expression) {
     _message = _becomeParentOf(expression);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitAssertStatement(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_condition, visitor);
-    _safelyVisitChild(message, visitor);
+    _condition?.accept(visitor);
+    message?.accept(visitor);
   }
 }
 
 /**
  * An assignment expression.
  *
  *    assignmentExpression ::=
  *        [Expression] operator [Expression]
  */
 class AssignmentExpressionImpl extends ExpressionImpl
@@ skipping 165 matching lines @@
       return null;
     }
     return parameters[0];
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitAssignmentExpression(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_leftHandSide, visitor);
-    _safelyVisitChild(_rightHandSide, visitor);
+    _leftHandSide?.accept(visitor);
+    _rightHandSide?.accept(visitor);
   }
 }
 
 /**
  * A node in the AST structure for a Dart program.
  */
 abstract class AstNodeImpl implements AstNode {
   /**
    * The parent of the node, or `null` if the node is the root of an AST
    * structure.
@@ skipping 92 matching lines @@
 
   /**
    * Make this node the parent of the given [child] node. Return the child node.
    */
   AstNode _becomeParentOf(AstNode child) {
     if (child != null) {
       (child as AstNodeImpl)._parent = this;
     }
     return child;
   }
-
-  /**
-   * If the given [child] is not `null`, use the given [visitor] to visit it.
-   */
-  void _safelyVisitChild(AstNode child, AstVisitor visitor) {
-    if (child != null) {
-      child.accept(visitor);
-    }
-  }
 }
 
 /**
  * An await expression.
  *
  *    awaitExpression ::=
  *        'await' [Expression]
  */
 class AwaitExpressionImpl extends ExpressionImpl implements AwaitExpression {
   /**
@@ skipping 38 matching lines @@
   }
 
   @override
   int get precedence => 0;
 
   @override
   accept(AstVisitor visitor) => visitor.visitAwaitExpression(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_expression, visitor);
+    _expression?.accept(visitor);
   }
 }
 
 /**
  * A binary (infix) expression.
  *
  *    binaryExpression ::=
  *        [Expression] [Token] [Expression]
  */
 class BinaryExpressionImpl extends ExpressionImpl implements BinaryExpression {
@@ skipping 109 matching lines @@
       return null;
     }
     return parameters[0];
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitBinaryExpression(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_leftOperand, visitor);
-    _safelyVisitChild(_rightOperand, visitor);
+    _leftOperand?.accept(visitor);
+    _rightOperand?.accept(visitor);
   }
 }
 
 /**
  * A function body that consists of a block of statements.
  *
  *    blockFunctionBody ::=
  *        ('async' | 'async' '*' | 'sync' '*')? [Block]
  */
 class BlockFunctionBodyImpl extends FunctionBodyImpl
@@ skipping 57 matching lines @@
   bool get isGenerator => star != null;
 
   @override
   bool get isSynchronous => keyword == null || keyword.lexeme != Parser.ASYNC;
 
   @override
   accept(AstVisitor visitor) => visitor.visitBlockFunctionBody(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_block, visitor);
+    _block?.accept(visitor);
   }
 }
 
 /**
  * A sequence of statements.
  *
  *    block ::=
  *        '{' statement* '}'
  */
 class BlockImpl extends StatementImpl implements Block {
@@ skipping 151 matching lines @@
   @override
   void set label(SimpleIdentifier identifier) {
     _label = _becomeParentOf(identifier);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitBreakStatement(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_label, visitor);
+    _label?.accept(visitor);
   }
 }
 
 /**
  * A sequence of cascaded expressions: expressions that share a common target.
  * There are three kinds of expressions that can be used in a cascade
  * expression: [IndexExpression], [MethodInvocation] and [PropertyAccess].
  *
  *    cascadeExpression ::=
  *        [Expression] cascadeSection*
@@ skipping 50 matching lines @@
   @override
   void set target(Expression target) {
     _target = _becomeParentOf(target);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitCascadeExpression(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_target, visitor);
+    _target?.accept(visitor);
     _cascadeSections.accept(visitor);
   }
 }
 
 /**
  * A catch clause within a try statement.
  *
  *    onPart ::=
  *        catchPart [Block]
  *      | 'on' type catchPart? [Block]
@@ skipping 133 matching lines @@
   @override
   void set stackTraceParameter(SimpleIdentifier parameter) {
     _stackTraceParameter = _becomeParentOf(parameter);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitCatchClause(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_exceptionType, visitor);
-    _safelyVisitChild(_exceptionParameter, visitor);
-    _safelyVisitChild(_stackTraceParameter, visitor);
-    _safelyVisitChild(_body, visitor);
+    _exceptionType?.accept(visitor);
+    _exceptionParameter?.accept(visitor);
+    _stackTraceParameter?.accept(visitor);
+    _body?.accept(visitor);
   }
 }
 
 /**
  * Helper class to allow iteration of child entities of an AST node.
  */
 class ChildEntities extends Object with IterableMixin implements Iterable {
   /**
    * The list of child entities to be iterated over.
    */
@@ skipping 246 matching lines @@
           return method;
         }
       }
     }
     return null;
   }
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_name, visitor);
-    _safelyVisitChild(_typeParameters, visitor);
-    _safelyVisitChild(_extendsClause, visitor);
-    _safelyVisitChild(_withClause, visitor);
-    _safelyVisitChild(_implementsClause, visitor);
-    _safelyVisitChild(_nativeClause, visitor);
+    _name?.accept(visitor);
+    _typeParameters?.accept(visitor);
+    _extendsClause?.accept(visitor);
+    _withClause?.accept(visitor);
+    _implementsClause?.accept(visitor);
+    _nativeClause?.accept(visitor);
     members.accept(visitor);
   }
 }
 
 /**
  * A node that declares a name within the scope of a class.
  */
 abstract class ClassMemberImpl extends DeclarationImpl implements ClassMember {
   /**
    * Initialize a newly created member of a class. Either or both of the
@@ skipping 134 matching lines @@
   void set withClause(WithClause withClause) {
     _withClause = _becomeParentOf(withClause);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitClassTypeAlias(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_name, visitor);
-    _safelyVisitChild(_typeParameters, visitor);
-    _safelyVisitChild(_superclass, visitor);
-    _safelyVisitChild(_withClause, visitor);
-    _safelyVisitChild(_implementsClause, visitor);
+    _name?.accept(visitor);
+    _typeParameters?.accept(visitor);
+    _superclass?.accept(visitor);
+    _withClause?.accept(visitor);
+    _implementsClause?.accept(visitor);
   }
 }
 
 /**
  * A combinator associated with an import or export directive.
  *
  *    combinator ::=
  *        [HideCombinator]
  *      | [ShowCombinator]
  */
@@ skipping 161 matching lines @@
   @override
   void set identifier(Identifier identifier) {
     _identifier = _becomeParentOf(identifier);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitCommentReference(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_identifier, visitor);
+    _identifier?.accept(visitor);
   }
 }
 
 /**
  * The possible types of comments that are recognized by the parser.
  */
 class CommentType {
   /**
    * A block comment.
    */
@@ skipping 164 matching lines @@
     Directive lastDirective = _directives[_directives.length - 1];
     CompilationUnitMember firstDeclaration = _declarations[0];
     return lastDirective.offset < firstDeclaration.offset;
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitCompilationUnit(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_scriptTag, visitor);
+    _scriptTag?.accept(visitor);
     if (_directivesAreBeforeDeclarations) {
       _directives.accept(visitor);
       _declarations.accept(visitor);
     } else {
       for (AstNode child in sortedDirectivesAndDeclarations) {
         child.accept(visitor);
       }
     }
   }
 }
@@ skipping 105 matching lines @@
   @override
   void set thenExpression(Expression expression) {
     _thenExpression = _becomeParentOf(expression);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitConditionalExpression(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_condition, visitor);
-    _safelyVisitChild(_thenExpression, visitor);
-    _safelyVisitChild(_elseExpression, visitor);
+    _condition?.accept(visitor);
+    _thenExpression?.accept(visitor);
+    _elseExpression?.accept(visitor);
   }
 }
 
 /**
  * A configuration in either an import or export directive.
  *
  *     configuration ::=
  *         'if' '(' test ')' uri
  *
  *     test ::=
@@ skipping 66 matching lines @@
   @override
   void set value(StringLiteral value) {
     _value = _becomeParentOf(value);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitConfiguration(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_name, visitor);
-    _safelyVisitChild(_value, visitor);
-    _safelyVisitChild(_libraryUri, visitor);
+    _name?.accept(visitor);
+    _value?.accept(visitor);
+    _libraryUri?.accept(visitor);
   }
 }
 
 /**
  * A constructor declaration.
  *
  *    constructorDeclaration ::=
  *        constructorSignature [FunctionBody]?
  *      | constructorName formalParameterList ':' 'this' ('.' [SimpleIdentifier])? arguments
  *
@@ skipping 205 matching lines @@
   void set returnType(Identifier typeName) {
     _returnType = _becomeParentOf(typeName);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitConstructorDeclaration(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_returnType, visitor);
-    _safelyVisitChild(_name, visitor);
-    _safelyVisitChild(_parameters, visitor);
+    _returnType?.accept(visitor);
+    _name?.accept(visitor);
+    _parameters?.accept(visitor);
     _initializers.accept(visitor);
-    _safelyVisitChild(_redirectedConstructor, visitor);
-    _safelyVisitChild(_body, visitor);
+    _redirectedConstructor?.accept(visitor);
+    _body?.accept(visitor);
   }
 }
 
 /**
  * The initialization of a field within a constructor's initialization list.
  *
  *    fieldInitializer ::=
  *        ('this' '.')? [SimpleIdentifier] '=' [Expression]
  */
 class ConstructorFieldInitializerImpl extends ConstructorInitializerImpl
@@ skipping 71 matching lines @@
   @override
   void set fieldName(SimpleIdentifier identifier) {
     _fieldName = _becomeParentOf(identifier);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitConstructorFieldInitializer(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_fieldName, visitor);
-    _safelyVisitChild(_expression, visitor);
+    _fieldName?.accept(visitor);
+    _expression?.accept(visitor);
   }
 }
 
 /**
  * A node that can occur in the initializer list of a constructor declaration.
  *
  *    constructorInitializer ::=
  *        [SuperConstructorInvocation]
  *      | [ConstructorFieldInitializer]
  *      | [RedirectingConstructorInvocation]
@@ skipping 72 matching lines @@
   @override
   void set type(TypeName type) {
     _type = _becomeParentOf(type);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitConstructorName(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_type, visitor);
-    _safelyVisitChild(_name, visitor);
+    _type?.accept(visitor);
+    _name?.accept(visitor);
   }
 }
 
 /**
  * A continue statement.
  *
  *    continueStatement ::=
  *        'continue' [SimpleIdentifier]? ';'
  */
 class ContinueStatementImpl extends StatementImpl implements ContinueStatement {
@@ skipping 49 matching lines @@
   @override
   void set label(SimpleIdentifier identifier) {
     _label = _becomeParentOf(identifier);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitContinueStatement(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_label, visitor);
+    _label?.accept(visitor);
   }
 }
 
 /**
  * A node that represents the declaration of one or more names. Each declared
  * name is visible within a name scope.
  */
 abstract class DeclarationImpl extends AnnotatedNodeImpl
     implements Declaration {
   /**
@@ skipping 94 matching lines @@
   void set type(TypeName typeName) {
     _type = _becomeParentOf(typeName);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitDeclaredIdentifier(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_type, visitor);
-    _safelyVisitChild(_identifier, visitor);
+    _type?.accept(visitor);
+    _identifier?.accept(visitor);
   }
 }
 
 /**
  * A formal parameter with a default value. There are two kinds of parameters
  * that are both represented by this class: named formal parameters and
  * positional formal parameters.
  *
  *    defaultFormalParameter ::=
  *        [NormalFormalParameter] ('=' [Expression])?
@@ skipping 78 matching lines @@
   @override
   void set parameter(NormalFormalParameter formalParameter) {
     _parameter = _becomeParentOf(formalParameter);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitDefaultFormalParameter(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_parameter, visitor);
-    _safelyVisitChild(_defaultValue, visitor);
+    _parameter?.accept(visitor);
+    _defaultValue?.accept(visitor);
   }
 }
 
 /**
  * A node that represents a directive.
  *
  *    directive ::=
  *        [ExportDirective]
  *      | [ImportDirective]
  *      | [LibraryDirective]
@@ skipping 108 matching lines @@
   }
 
   @override
   Token get endToken => semicolon;
 
   @override
   accept(AstVisitor visitor) => visitor.visitDoStatement(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_body, visitor);
-    _safelyVisitChild(_condition, visitor);
+    _body?.accept(visitor);
+    _condition?.accept(visitor);
   }
 }
 
 /**
  * A dotted name, used in a configuration within an import or export directive.
  *
  *    dottedName ::=
  *        [SimpleIdentifier] ('.' [SimpleIdentifier])*
  */
 class DottedNameImpl extends AstNodeImpl implements DottedName {
@@ skipping 193 matching lines @@
   void set name(SimpleIdentifier name) {
     _name = _becomeParentOf(name);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitEnumConstantDeclaration(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_name, visitor);
+    _name?.accept(visitor);
   }
 }
 
 /**
  * The declaration of an enumeration.
  *
  *    enumType ::=
  *        metadata 'enum' [SimpleIdentifier] '{' [SimpleIdentifier] (',' [SimpleIdentifier])* (',')? '}'
  */
 class EnumDeclarationImpl extends NamedCompilationUnitMemberImpl
@@ skipping 60 matching lines @@
 
   @override
   Token get firstTokenAfterCommentAndMetadata => enumKeyword;
 
   @override
   accept(AstVisitor visitor) => visitor.visitEnumDeclaration(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_name, visitor);
+    _name?.accept(visitor);
     _constants.accept(visitor);
   }
 }
 
 /**
  * Ephemeral identifiers are created as needed to mimic the presence of an empty
  * identifier.
  */
 class EphemeralIdentifier extends SimpleIdentifierImpl {
   EphemeralIdentifier(AstNode parent, int location)
@@ skipping 132 matching lines @@
   bool get isAsynchronous => keyword != null;
 
   @override
   bool get isSynchronous => keyword == null;
 
   @override
   accept(AstVisitor visitor) => visitor.visitExpressionFunctionBody(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_expression, visitor);
+    _expression?.accept(visitor);
   }
 }
 
 /**
  * A node that represents an expression.
  *
  *    expression ::=
  *        [AssignmentExpression]
  *      | [ConditionalExpression] cascadeSection*
  *      | [ThrowExpression]
@@ skipping 142 matching lines @@
   }
 
   @override
   bool get isSynthetic => _expression.isSynthetic && semicolon.isSynthetic;
 
   @override
   accept(AstVisitor visitor) => visitor.visitExpressionStatement(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_expression, visitor);
+    _expression?.accept(visitor);
   }
 }
 
 /**
  * The "extends" clause in a class declaration.
  *
  *    extendsClause ::=
  *        'extends' [TypeName]
  */
 class ExtendsClauseImpl extends AstNodeImpl implements ExtendsClause {
@@ skipping 31 matching lines @@
   @override
   void set superclass(TypeName name) {
     _superclass = _becomeParentOf(name);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitExtendsClause(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_superclass, visitor);
+    _superclass?.accept(visitor);
   }
 }
 
 /**
  * The declaration of one or more fields of the same type.
  *
  *    fieldDeclaration ::=
  *        'static'? [VariableDeclarationList] ';'
  */
 class FieldDeclarationImpl extends ClassMemberImpl implements FieldDeclaration {
@@ skipping 55 matching lines @@
 
   @override
   bool get isStatic => staticKeyword != null;
 
   @override
   accept(AstVisitor visitor) => visitor.visitFieldDeclaration(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_fieldList, visitor);
+    _fieldList?.accept(visitor);
   }
 }
 
 /**
  * A field formal parameter.
  *
  *    fieldFormalParameter ::=
  *        ('final' [TypeName] | 'const' [TypeName] | 'var' | [TypeName])?
  *        'this' '.' [SimpleIdentifier] ([TypeParameterList]? [FormalParameterList])?
  */
@@ skipping 121 matching lines @@
   void set typeParameters(TypeParameterList typeParameters) {
     _typeParameters = _becomeParentOf(typeParameters);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitFieldFormalParameter(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_type, visitor);
-    _safelyVisitChild(identifier, visitor);
-    _safelyVisitChild(_typeParameters, visitor);
-    _safelyVisitChild(_parameters, visitor);
+    _type?.accept(visitor);
+    identifier?.accept(visitor);
+    _typeParameters?.accept(visitor);
+    _parameters?.accept(visitor);
   }
 }
 
 /**
  * A for-each statement.
  *
  *    forEachStatement ::=
  *        'await'? 'for' '(' [DeclaredIdentifier] 'in' [Expression] ')' [Block]
  *      | 'await'? 'for' '(' [SimpleIdentifier] 'in' [Expression] ')' [Block]
  */
@@ skipping 136 matching lines @@
   @override
   void set loopVariable(DeclaredIdentifier variable) {
     _loopVariable = _becomeParentOf(variable);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitForEachStatement(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_loopVariable, visitor);
-    _safelyVisitChild(_identifier, visitor);
-    _safelyVisitChild(_iterable, visitor);
-    _safelyVisitChild(_body, visitor);
+    _loopVariable?.accept(visitor);
+    _identifier?.accept(visitor);
+    _iterable?.accept(visitor);
+    _body?.accept(visitor);
   }
 }
 
 /**
  * A node representing a parameter to a function.
  *
  *    formalParameter ::=
  *        [NormalFormalParameter]
  *      | [DefaultFormalParameter]
  */
@@ skipping 277 matching lines @@
   @override
   void set variables(VariableDeclarationList variableList) {
     _variableList = _becomeParentOf(variableList);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitForStatement(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_variableList, visitor);
-    _safelyVisitChild(_initialization, visitor);
-    _safelyVisitChild(_condition, visitor);
+    _variableList?.accept(visitor);
+    _initialization?.accept(visitor);
+    _condition?.accept(visitor);
     _updaters.accept(visitor);
-    _safelyVisitChild(_body, visitor);
+    _body?.accept(visitor);
   }
 }
 
 /**
  * A node representing the body of a function or method.
  *
  *    functionBody ::=
  *        [BlockFunctionBody]
  *      | [EmptyFunctionBody]
  *      | [ExpressionFunctionBody]
@@ skipping 166 matching lines @@
   void set returnType(TypeName returnType) {
     _returnType = _becomeParentOf(returnType);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitFunctionDeclaration(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_returnType, visitor);
-    _safelyVisitChild(_name, visitor);
-    _safelyVisitChild(_functionExpression, visitor);
+    _returnType?.accept(visitor);
+    _name?.accept(visitor);
+    _functionExpression?.accept(visitor);
   }
 }
 
 /**
  * A [FunctionDeclaration] used as a statement.
  */
 class FunctionDeclarationStatementImpl extends StatementImpl
     implements FunctionDeclarationStatement {
   /**
    * The function declaration being wrapped.
@@ skipping 22 matching lines @@
   @override
   void set functionDeclaration(FunctionDeclaration functionDeclaration) {
     _functionDeclaration = _becomeParentOf(functionDeclaration);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitFunctionDeclarationStatement(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_functionDeclaration, visitor);
+    _functionDeclaration?.accept(visitor);
   }
 }
 
 /**
  * A function expression.
  *
  *    functionExpression ::=
  *        [TypeParameterList]? [FormalParameterList] [FunctionBody]
  */
 class FunctionExpressionImpl extends ExpressionImpl
@@ skipping 86 matching lines @@
   @override
   void set typeParameters(TypeParameterList typeParameters) {
     _typeParameters = _becomeParentOf(typeParameters);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitFunctionExpression(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_typeParameters, visitor);
-    _safelyVisitChild(_parameters, visitor);
-    _safelyVisitChild(_body, visitor);
+    _typeParameters?.accept(visitor);
+    _parameters?.accept(visitor);
+    _body?.accept(visitor);
   }
 }
 
 /**
  * The invocation of a function resulting from evaluating an expression.
  * Invocations of methods and other forms of functions are represented by
  * [MethodInvocation] nodes. Invocations of getters and setters are represented
  * by either [PrefixedIdentifier] or [PropertyAccess] nodes.
  *
  *    functionExpressionInvocation ::=
@@ skipping 59 matching lines @@
   }
 
   @override
   int get precedence => 15;
 
   @override
   accept(AstVisitor visitor) => visitor.visitFunctionExpressionInvocation(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_function, visitor);
-    _safelyVisitChild(_typeArguments, visitor);
-    _safelyVisitChild(_argumentList, visitor);
+    _function?.accept(visitor);
+    _typeArguments?.accept(visitor);
+    _argumentList?.accept(visitor);
   }
 }
 
 /**
  * A function type alias.
  *
  *    functionTypeAlias ::=
  *        functionPrefix [TypeParameterList]? [FormalParameterList] ';'
  *
  *    functionPrefix ::=
@@ skipping 75 matching lines @@
   void set typeParameters(TypeParameterList typeParameters) {
     _typeParameters = _becomeParentOf(typeParameters);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitFunctionTypeAlias(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_returnType, visitor);
-    _safelyVisitChild(_name, visitor);
-    _safelyVisitChild(_typeParameters, visitor);
-    _safelyVisitChild(_parameters, visitor);
+    _returnType?.accept(visitor);
+    _name?.accept(visitor);
+    _typeParameters?.accept(visitor);
+    _parameters?.accept(visitor);
   }
 }
 
 /**
  * A function-typed formal parameter.
  *
  *    functionSignature ::=
  *        [TypeName]? [SimpleIdentifier] [TypeParameterList]? [FormalParameterList]
  */
 class FunctionTypedFormalParameterImpl extends NormalFormalParameterImpl
@@ skipping 78 matching lines @@
   void set typeParameters(TypeParameterList typeParameters) {
     _typeParameters = _becomeParentOf(typeParameters);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitFunctionTypedFormalParameter(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_returnType, visitor);
-    _safelyVisitChild(identifier, visitor);
-    _safelyVisitChild(_typeParameters, visitor);
-    _safelyVisitChild(_parameters, visitor);
+    _returnType?.accept(visitor);
+    identifier?.accept(visitor);
+    _typeParameters?.accept(visitor);
+    _parameters?.accept(visitor);
   }
 }
 
 /**
  * A combinator that restricts the names being imported to those that are not in
  * a given list.
  *
  *    hideCombinator ::=
  *        'hide' [SimpleIdentifier] (',' [SimpleIdentifier])*
  */
@@ skipping 160 matching lines @@
   @override
   void set thenStatement(Statement statement) {
     _thenStatement = _becomeParentOf(statement);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitIfStatement(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_condition, visitor);
-    _safelyVisitChild(_thenStatement, visitor);
-    _safelyVisitChild(_elseStatement, visitor);
+    _condition?.accept(visitor);
+    _thenStatement?.accept(visitor);
+    _elseStatement?.accept(visitor);
   }
 }
 
 /**
  * The "implements" clause in an class declaration.
  *
  *    implementsClause ::=
  *        'implements' [TypeName] (',' [TypeName])*
  */
 class ImplementsClauseImpl extends AstNodeImpl implements ImplementsClause {
@@ skipping 119 matching lines @@
     }
     return element.importedLibrary;
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitImportDirective(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_prefix, visitor);
+    _prefix?.accept(visitor);
     combinators.accept(visitor);
   }
 }
 
 /**
  * An index expression.
  *
  *    indexExpression ::=
  *        [Expression] '[' [Expression] ']'
  */
@@ skipping 198 matching lines @@
     } else if (parent is PostfixExpression) {
       return true;
     } else if (parent is AssignmentExpression) {
       return identical(parent.leftHandSide, this);
     }
     return false;
   }
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_target, visitor);
-    _safelyVisitChild(_index, visitor);
+    _target?.accept(visitor);
+    _index?.accept(visitor);
   }
 }
 
 /**
  * An instance creation expression.
  *
  *    newExpression ::=
  *        ('new' | 'const') [TypeName] ('.' [SimpleIdentifier])? [ArgumentList]
  */
 class InstanceCreationExpressionImpl extends ExpressionImpl
@@ skipping 66 matching lines @@
       (keyword as KeywordToken).keyword == Keyword.CONST;
 
   @override
   int get precedence => 16;
 
   @override
   accept(AstVisitor visitor) => visitor.visitInstanceCreationExpression(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_constructorName, visitor);
-    _safelyVisitChild(_argumentList, visitor);
+    _constructorName?.accept(visitor);
+    _argumentList?.accept(visitor);
   }
 }
 
 /**
  * An integer literal expression.
  *
  *    integerLiteral ::=
  *        decimalIntegerLiteral
  *      | hexadecimalIntegerLiteral
  *
@@ skipping 110 matching lines @@
   @override
   void set expression(Expression expression) {
     _expression = _becomeParentOf(expression);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitInterpolationExpression(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_expression, visitor);
+    _expression?.accept(visitor);
   }
 }
 
 /**
  * A non-empty substring of an interpolated string.
  *
  *    interpolationString ::=
  *        characters
  */
 class InterpolationStringImpl extends InterpolationElementImpl
@@ skipping 161 matching lines @@
   @override
   void set type(TypeName name) {
     _type = _becomeParentOf(name);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitIsExpression(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_expression, visitor);
-    _safelyVisitChild(_type, visitor);
+    _expression?.accept(visitor);
+    _type?.accept(visitor);
   }
 }
 
 /**
  * A statement that has a label associated with them.
  *
  *    labeledStatement ::=
  *       [Label]+ [Statement]
  */
 class LabeledStatementImpl extends StatementImpl implements LabeledStatement {
@@ skipping 44 matching lines @@
 
   @override
   Statement get unlabeled => _statement.unlabeled;
 
   @override
   accept(AstVisitor visitor) => visitor.visitLabeledStatement(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     _labels.accept(visitor);
-    _safelyVisitChild(_statement, visitor);
+    _statement?.accept(visitor);
   }
 }
 
 /**
  * A label on either a [LabeledStatement] or a [NamedExpression].
  *
  *    label ::=
  *        [SimpleIdentifier] ':'
  */
 class LabelImpl extends AstNodeImpl implements Label {
@@ skipping 30 matching lines @@
   @override
   void set label(SimpleIdentifier label) {
     _label = _becomeParentOf(label);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitLabel(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_label, visitor);
+    _label?.accept(visitor);
   }
 }
 
 /**
  * A library directive.
  *
  *    libraryDirective ::=
  *        [Annotation] 'library' [Identifier] ';'
  */
 class LibraryDirectiveImpl extends DirectiveImpl implements LibraryDirective {
@@ skipping 45 matching lines @@
   void set name(LibraryIdentifier name) {
     _name = _becomeParentOf(name);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitLibraryDirective(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_name, visitor);
+    _name?.accept(visitor);
   }
 }
 
 /**
  * The identifier for a library.
  *
  *    libraryIdentifier ::=
  *        [SimpleIdentifier] ('.' [SimpleIdentifier])*
  */
 class LibraryIdentifierImpl extends IdentifierImpl
@@ skipping 222 matching lines @@
   @override
   void set value(Expression expression) {
     _value = _becomeParentOf(expression);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitMapLiteralEntry(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_key, visitor);
-    _safelyVisitChild(_value, visitor);
+    _key?.accept(visitor);
+    _value?.accept(visitor);
   }
 }
 
 /**
  * A literal map.
  *
  *    mapLiteral ::=
  *        'const'? ('<' [TypeName] (',' [TypeName])* '>')?
  *        '{' ([MapLiteralEntry] (',' [MapLiteralEntry])* ','?)? '}'
  */
@@ skipping 266 matching lines @@
   void set typeParameters(TypeParameterList typeParameters) {
     _typeParameters = _becomeParentOf(typeParameters);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitMethodDeclaration(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_returnType, visitor);
-    _safelyVisitChild(_name, visitor);
-    _safelyVisitChild(_typeParameters, visitor);
-    _safelyVisitChild(_parameters, visitor);
-    _safelyVisitChild(_body, visitor);
+    _returnType?.accept(visitor);
+    _name?.accept(visitor);
+    _typeParameters?.accept(visitor);
+    _parameters?.accept(visitor);
+    _body?.accept(visitor);
   }
 }
 
 /**
  * The invocation of either a function or a method. Invocations of functions
  * resulting from evaluating an expression are represented by
  * [FunctionExpressionInvocation] nodes. Invocations of getters and setters are
  * represented by either [PrefixedIdentifier] or [PropertyAccess] nodes.
  *
  *    methodInvocation ::=
@@ skipping 95 matching lines @@
   @override
   void set target(Expression expression) {
     _target = _becomeParentOf(expression);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitMethodInvocation(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_target, visitor);
-    _safelyVisitChild(_methodName, visitor);
-    _safelyVisitChild(_typeArguments, visitor);
-    _safelyVisitChild(_argumentList, visitor);
+    _target?.accept(visitor);
+    _methodName?.accept(visitor);
+    _typeArguments?.accept(visitor);
+    _argumentList?.accept(visitor);
   }
 }
 
 /**
  * A node that declares a single name within the scope of a compilation unit.
  */
 abstract class NamedCompilationUnitMemberImpl extends CompilationUnitMemberImpl
     implements NamedCompilationUnitMember {
   /**
    * The name of the member being declared.
@@ skipping 82 matching lines @@
   }
 
   @override
   int get precedence => 0;
 
   @override
   accept(AstVisitor visitor) => visitor.visitNamedExpression(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_name, visitor);
-    _safelyVisitChild(_expression, visitor);
+    _name?.accept(visitor);
+    _expression?.accept(visitor);
   }
 }
 
 /**
  * A node that represents a directive that impacts the namespace of a library.
  *
  *    directive ::=
  *        [ExportDirective]
  *      | [ImportDirective]
  */
@@ skipping 98 matching lines @@
   @override
   void set name(StringLiteral name) {
     _name = _becomeParentOf(name);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitNativeClause(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_name, visitor);
+    _name?.accept(visitor);
   }
 }
 
 /**
  * A function body that consists of a native keyword followed by a string
  * literal.
  *
  *    nativeFunctionBody ::=
  *        'native' [SimpleStringLiteral] ';'
  */
@@ skipping 44 matching lines @@
   @override
   void set stringLiteral(StringLiteral stringLiteral) {
     _stringLiteral = _becomeParentOf(stringLiteral);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitNativeFunctionBody(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_stringLiteral, visitor);
+    _stringLiteral?.accept(visitor);
   }
 }
 
 /**
  * A list of AST nodes that have a common parent.
  */
 class NodeListImpl<E extends AstNode> extends Object
     with ListMixin<E>
     implements NodeList<E> {
   /**
@@ skipping 203 matching lines @@
     return result;
   }
 
   @override
   void visitChildren(AstVisitor visitor) {
     //
     // Note that subclasses are responsible for visiting the identifier because
     // they often need to visit other nodes before visiting the identifier.
     //
     if (_commentIsBeforeAnnotations()) {
-      _safelyVisitChild(_comment, visitor);
+      _comment?.accept(visitor);
       _metadata.accept(visitor);
     } else {
       for (AstNode child in sortedCommentAndAnnotations) {
         child.accept(visitor);
       }
     }
   }
 
   /**
    * Return `true` if the comment is lexically before any annotations.
@@ skipping 94 matching lines @@
   }
 
   @override
   int get precedence => 15;
 
   @override
   accept(AstVisitor visitor) => visitor.visitParenthesizedExpression(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_expression, visitor);
+    _expression?.accept(visitor);
   }
 }
 
 /**
  * A part directive.
  *
  *    partDirective ::=
  *        [Annotation] 'part' [StringLiteral] ';'
  */
 class PartDirectiveImpl extends UriBasedDirectiveImpl implements PartDirective {
@@ skipping 107 matching lines @@
   void set libraryName(LibraryIdentifier libraryName) {
     _libraryName = _becomeParentOf(libraryName);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitPartOfDirective(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_libraryName, visitor);
+    _libraryName?.accept(visitor);
   }
 }
 
 /**
  * A postfix unary expression.
  *
  *    postfixExpression ::=
  *        [Expression] [Token]
  */
 class PostfixExpressionImpl extends ExpressionImpl
@@ skipping 95 matching lines @@
       return null;
     }
     return parameters[0];
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitPostfixExpression(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_operand, visitor);
+    _operand?.accept(visitor);
   }
 }
 
 /**
  * An identifier that is prefixed or an access to an object property where the
  * target of the property access is a simple identifier.
  *
  *    prefixedIdentifier ::=
  *        [SimpleIdentifier] '.' [SimpleIdentifier]
  */
@@ skipping 92 matching lines @@
       return null;
     }
     return _identifier.staticElement;
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitPrefixedIdentifier(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_prefix, visitor);
-    _safelyVisitChild(_identifier, visitor);
+    _prefix?.accept(visitor);
+    _identifier?.accept(visitor);
   }
 }
 
 /**
  * A prefix unary expression.
  *
  *    prefixExpression ::=
  *        [Token] [Expression]
  */
 class PrefixExpressionImpl extends ExpressionImpl implements PrefixExpression {
@@ skipping 90 matching lines @@
       return null;
     }
     return parameters[0];
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitPrefixExpression(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_operand, visitor);
+    _operand?.accept(visitor);
   }
 }
 
 /**
  * The access of a property of an object.
  *
  * Note, however, that accesses to properties of objects can also be represented
  * as [PrefixedIdentifier] nodes in cases where the target is also a simple
  * identifier.
  *
@@ skipping 79 matching lines @@
   @override
   void set target(Expression expression) {
     _target = _becomeParentOf(expression);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitPropertyAccess(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_target, visitor);
-    _safelyVisitChild(_propertyName, visitor);
+    _target?.accept(visitor);
+    _propertyName?.accept(visitor);
   }
 }
 
 /**
  * The invocation of a constructor in the same class from within a constructor's
  * initialization list.
  *
  *    redirectingConstructorInvocation ::=
  *        'this' ('.' identifier)? arguments
  */
@@ skipping 67 matching lines @@
 
   @override
   Token get endToken => _argumentList.endToken;
 
   @override
   accept(AstVisitor visitor) =>
       visitor.visitRedirectingConstructorInvocation(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_constructorName, visitor);
-    _safelyVisitChild(_argumentList, visitor);
+    _constructorName?.accept(visitor);
+    _argumentList?.accept(visitor);
   }
 }
 
 /**
  * A rethrow expression.
  *
  *    rethrowExpression ::=
  *        'rethrow'
  */
 class RethrowExpressionImpl extends ExpressionImpl
@@ skipping 77 matching lines @@
   @override
   void set expression(Expression expression) {
     _expression = _becomeParentOf(expression);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitReturnStatement(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_expression, visitor);
+    _expression?.accept(visitor);
   }
 }
 
 /**
  * A script tag that can optionally occur at the beginning of a compilation unit.
  *
  *    scriptTag ::=
  *        '#!' (~NEWLINE)* NEWLINE
  */
 class ScriptTagImpl extends AstNodeImpl implements ScriptTag {
@@ skipping 135 matching lines @@
   void set type(TypeName typeName) {
     _type = _becomeParentOf(typeName);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitSimpleFormalParameter(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_type, visitor);
-    _safelyVisitChild(identifier, visitor);
+    _type?.accept(visitor);
+    identifier?.accept(visitor);
   }
 }
 
 /**
  * A simple identifier.
  *
  *    simpleIdentifier ::=
  *        initialCharacter internalCharacter*
  *
  *    initialCharacter ::= '_' | '$' | letter
@@ skipping 682 matching lines @@
   }
 
   @override
   Token get endToken => _argumentList.endToken;
 
   @override
   accept(AstVisitor visitor) => visitor.visitSuperConstructorInvocation(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_constructorName, visitor);
-    _safelyVisitChild(_argumentList, visitor);
+    _constructorName?.accept(visitor);
+    _argumentList?.accept(visitor);
   }
 }
 
 /**
  * A super expression.
  *
  *    superExpression ::=
  *        'super'
  */
 class SuperExpressionImpl extends ExpressionImpl implements SuperExpression {
@@ skipping 65 matching lines @@
   void set expression(Expression expression) {
     _expression = _becomeParentOf(expression);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitSwitchCase(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     labels.accept(visitor);
-    _safelyVisitChild(_expression, visitor);
+    _expression?.accept(visitor);
     statements.accept(visitor);
   }
 }
 
 /**
  * The default case in a switch statement.
  *
  *    switchDefault ::=
  *        [SimpleIdentifier]* 'default' ':' [Statement]*
  */
@@ skipping 168 matching lines @@
   }
 
   @override
   NodeList<SwitchMember> get members => _members;
 
   @override
   accept(AstVisitor visitor) => visitor.visitSwitchStatement(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_expression, visitor);
+    _expression?.accept(visitor);
     _members.accept(visitor);
   }
 }
 
 /**
  * A symbol literal expression.
  *
  *    symbolLiteral ::=
  *        '#' (operator | (identifier ('.' identifier)*))
  */
@@ skipping 120 matching lines @@
   }
 
   @override
   int get precedence => 0;
 
   @override
   accept(AstVisitor visitor) => visitor.visitThrowExpression(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_expression, visitor);
+    _expression?.accept(visitor);
   }
 }
 
 /**
  * The declaration of one or more top-level variables of the same type.
  *
  *    topLevelVariableDeclaration ::=
  *        ('final' | 'const') type? staticFinalDeclarationList ';'
  *      | variableDeclaration ';'
  */
@@ skipping 40 matching lines @@
   void set variables(VariableDeclarationList variables) {
     _variableList = _becomeParentOf(variables);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitTopLevelVariableDeclaration(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_variableList, visitor);
+    _variableList?.accept(visitor);
   }
 }
 
 /**
  * A try statement.
  *
  *    tryStatement ::=
  *        'try' [Block] ([CatchClause]+ finallyClause? | finallyClause)
  *
  *    finallyClause ::=
@@ skipping 79 matching lines @@
   @override
   void set finallyBlock(Block block) {
     _finallyBlock = _becomeParentOf(block);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitTryStatement(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_body, visitor);
+    _body?.accept(visitor);
     _catchClauses.accept(visitor);
-    _safelyVisitChild(_finallyBlock, visitor);
+    _finallyBlock?.accept(visitor);
   }
 }
 
 /**
  * The declaration of a type alias.
  *
  *    typeAlias ::=
  *        'typedef' typeAliasBody
  *
  *    typeAliasBody ::=
@@ skipping 118 matching lines @@
   @override
   void set typeArguments(TypeArgumentList typeArguments) {
     _typeArguments = _becomeParentOf(typeArguments);
   }
 
   ChildEntities get _childEntities =>
       new ChildEntities()..add(constKeyword)..add(_typeArguments);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_typeArguments, visitor);
+    _typeArguments?.accept(visitor);
   }
 }
 
 /**
  * The name of a type, which can optionally include type arguments.
  *
  *    typeName ::=
  *        [Identifier] typeArguments?
  */
 class TypeNameImpl extends AstNodeImpl implements TypeName {
@@ skipping 63 matching lines @@
   @override
   void set typeArguments(TypeArgumentList typeArguments) {
     _typeArguments = _becomeParentOf(typeArguments);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitTypeName(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_name, visitor);
-    _safelyVisitChild(_typeArguments, visitor);
+    _name?.accept(visitor);
+    _typeArguments?.accept(visitor);
   }
 }
 
 /**
  * A type parameter.
  *
  *    typeParameter ::=
  *        [SimpleIdentifier] ('extends' [TypeName])?
  */
 class TypeParameterImpl extends DeclarationImpl implements TypeParameter {
@@ skipping 61 matching lines @@
   void set name(SimpleIdentifier identifier) {
     _name = _becomeParentOf(identifier);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitTypeParameter(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_name, visitor);
-    _safelyVisitChild(_bound, visitor);
+    _name?.accept(visitor);
+    _bound?.accept(visitor);
   }
 }
 
 /**
  * Type parameters within a declaration.
  *
  *    typeParameterList ::=
  *        '<' [TypeParameter] (',' [TypeParameter])* '>'
  */
 class TypeParameterListImpl extends AstNodeImpl implements TypeParameterList {
@@ skipping 111 matching lines @@
       parseUriWithException(Uri.encodeFull(uriContent));
     } on URISyntaxException {
       return UriValidationCode.INVALID_URI;
     }
     return null;
   }
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_uri, visitor);
+    _uri?.accept(visitor);
   }
 }
 
 /**
  * Validation codes returned by [UriBasedDirective.validate].
  */
 class UriValidationCodeImpl implements UriValidationCode {
   static const UriValidationCode INVALID_URI =
       const UriValidationCodeImpl('INVALID_URI');
 
@@ skipping 124 matching lines @@
   void set name(SimpleIdentifier identifier) {
     _name = _becomeParentOf(identifier);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitVariableDeclaration(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_name, visitor);
-    _safelyVisitChild(_initializer, visitor);
+    _name?.accept(visitor);
+    _initializer?.accept(visitor);
   }
 }
 
 /**
  * The declaration of one or more variables of the same type.
  *
  *    variableDeclarationList ::=
  *        finalConstVarOrType [VariableDeclaration] (',' [VariableDeclaration])*
  *
  *    finalConstVarOrType ::=
@@ skipping 73 matching lines @@
 
   @override
   NodeList<VariableDeclaration> get variables => _variables;
 
   @override
   accept(AstVisitor visitor) => visitor.visitVariableDeclarationList(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     super.visitChildren(visitor);
-    _safelyVisitChild(_type, visitor);
+    _type?.accept(visitor);
     _variables.accept(visitor);
   }
 }
 
 /**
  * A list of variables that are being declared in a context where a statement is
  * required.
  *
  *    variableDeclarationStatement ::=
  *        [VariableDeclarationList] ';'
@@ skipping 34 matching lines @@
   @override
   void set variables(VariableDeclarationList variables) {
     _variableList = _becomeParentOf(variables);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitVariableDeclarationStatement(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_variableList, visitor);
+    _variableList?.accept(visitor);
   }
 }
 
 /**
  * A while statement.
  *
  *    whileStatement ::=
  *        'while' '(' [Expression] ')' [Statement]
  */
 class WhileStatementImpl extends StatementImpl implements WhileStatement {
@@ skipping 59 matching lines @@
   }
 
   @override
   Token get endToken => _body.endToken;
 
   @override
   accept(AstVisitor visitor) => visitor.visitWhileStatement(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_condition, visitor);
-    _safelyVisitChild(_body, visitor);
+    _condition?.accept(visitor);
+    _body?.accept(visitor);
   }
 }
 
 /**
  * The with clause in a class declaration.
  *
  *    withClause ::=
  *        'with' [TypeName] (',' [TypeName])*
  */
 class WithClauseImpl extends AstNodeImpl implements WithClause {
@@ skipping 103 matching lines @@
   @override
   void set expression(Expression expression) {
     _expression = _becomeParentOf(expression);
   }
 
   @override
   accept(AstVisitor visitor) => visitor.visitYieldStatement(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
-    _safelyVisitChild(_expression, visitor);
+    _expression?.accept(visitor);
   }
 }