Add missing checks for null imported/exportedLibraries.

pkg/analyzer/lib/src/generated/element_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 analyzer.src.generated.element_resolver;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/syntactic_entity.dart';
@@ skipping 608 matching lines @@
       propagatedElement = null;
     } else if (methodName.name == FunctionElement.LOAD_LIBRARY_NAME &&
         _isDeferredPrefix(target)) {
       if (node.operator.type == TokenType.QUESTION_PERIOD) {
         _resolver.errorReporter.reportErrorForNode(
             CompileTimeErrorCode.PREFIX_IDENTIFIER_NOT_FOLLOWED_BY_DOT,
             target,
             [(target as SimpleIdentifier).name]);
       }
       LibraryElement importedLibrary = _getImportedLibrary(target);
-      FunctionElement loadLibraryFunction = importedLibrary.loadLibraryFunction;
+      FunctionElement loadLibraryFunction =
+          importedLibrary?.loadLibraryFunction;
       methodName.staticElement = loadLibraryFunction;
       node.staticInvokeType = loadLibraryFunction.type;
       return null;
     } else {
       //
       // If this method invocation is of the form 'C.m' where 'C' is a class,
       // then we don't call resolveInvokedElement(...) which walks up the class
       // hierarchy, instead we just look for the member in the type only.  This
       // does not apply to conditional method invocation (i.e. 'C?.m(...)').
       //
@@ skipping 247 matching lines @@
   @override
   Object visitPrefixedIdentifier(PrefixedIdentifier node) {
     SimpleIdentifier prefix = node.prefix;
     SimpleIdentifier identifier = node.identifier;
     //
     // First, check the "lib.loadLibrary" case
     //
     if (identifier.name == FunctionElement.LOAD_LIBRARY_NAME &&
         _isDeferredPrefix(prefix)) {
       LibraryElement importedLibrary = _getImportedLibrary(prefix);
-      identifier.staticElement = importedLibrary.loadLibraryFunction;
+      identifier.staticElement = importedLibrary?.loadLibraryFunction;
       return null;
     }
     //
     // Check to see whether the prefix is really a prefix.
     //
     Element prefixElement = prefix.staticElement;
     if (prefixElement is PrefixElement) {
       Element element = _resolver.nameScope.lookup(node, _definingLibrary);
       if (element == null && identifier.inSetterContext()) {
         Identifier setterName = new PrefixedIdentifierImpl.temp(
@@ skipping 1740 matching lines @@
 
   @override
   Element get staticElement => null;
 
   @override
   dynamic/*=E*/ accept/*<E>*/(AstVisitor/*<E>*/ visitor) => null;
 
   @override
   void visitChildren(AstVisitor visitor) {}
 }