Check for potential null operand in Not expressions.

pkg/analyzer/lib/src/generated/resolver.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 engine.resolver;
 
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/scanner.dart';
 
@@ skipping 647 matching lines @@
 
   /**
    * Produce a hint if the given [condition] could have a value of `null`.
    */
   void _checkForPossibleNullCondition(Expression condition) {
     while (condition is ParenthesizedExpression) {
       condition = (condition as ParenthesizedExpression).expression;
     }
     if (condition is BinaryExpression) {
       _checkForPossibleNullConditionInBinaryExpression(condition);
+    } else if (condition is PrefixExpression) {
+      _checkForPossibleNullConditionInPrefixExpression(condition);
     } else {
       _checkForPossibleNullConditionInSimpleExpression(condition);
     }
   }
 
   /**
    * Produce a hint if any of the parts of the given binary [condition] could
    * have a value of `null`.
    */
   void _checkForPossibleNullConditionInBinaryExpression(
       BinaryExpression condition) {
     Token operator = condition.operator;
     if (operator != null &&
         (operator.type == TokenType.AMPERSAND_AMPERSAND ||
             operator.type == TokenType.BAR_BAR)) {
       _checkForPossibleNullCondition(condition.leftOperand);
       _checkForPossibleNullCondition(condition.rightOperand);
     }
   }
 
   /**
+   * Produce a hint if the operand of the given prefix [condition] could
+   * have a value of `null`.
+   */
+  void _checkForPossibleNullConditionInPrefixExpression(
+      PrefixExpression condition) {
+    if (condition.operator?.type == TokenType.BANG) {
+      _checkForPossibleNullCondition(condition.operand);
+    }
+  }
+
+  /**
    * Produce a hint if the given [condition] could have a value of `null`.
    */
   void _checkForPossibleNullConditionInSimpleExpression(Expression condition) {
     if (condition is MethodInvocation) {
       Token operator = condition.operator;
       if (operator != null && operator.type == TokenType.QUESTION_PERIOD) {
         _errorReporter.reportErrorForNode(
             HintCode.NULL_AWARE_IN_CONDITION, condition);
       }
     } else if (condition is PropertyAccess) {
@@ skipping 15352 matching lines @@
     nonFields.add(node);
     return null;
   }
 
   @override
   Object visitNode(AstNode node) => node.accept(TypeResolverVisitor_this);
 
   @override
   Object visitWithClause(WithClause node) => null;
 }