Fix for issue 21982

pkg/analyzer/lib/src/generated/element.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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.element;
 
 import 'dart:collection';
@@ skipping 2623 matching lines @@
 
   @override
   ConstructorDeclaration get node =>
       getNodeMatching((node) => node is ConstructorDeclaration);
 
   @override
   accept(ElementVisitor visitor) => visitor.visitConstructorElement(this);
 
   @override
   void appendTo(StringBuffer buffer) {
-    buffer.write(enclosingElement.displayName);
+    if (enclosingElement == null) {
+      String message;
+      String name = displayName;
+      if (name != null && !name.isEmpty) {
+        message = 'Found constructor element named $name with no enclosing element';
+      } else {
+        message = 'Found unnamed constructor element with no enclosing element';
+      }
+      AnalysisEngine.instance.instrumentationService.logError(message);
+      buffer.write('<unknown class>');
+    } else {
+      buffer.write(enclosingElement.displayName);
+    }
     String name = displayName;
     if (name != null && !name.isEmpty) {
       buffer.write(".");
       buffer.write(name);
     }
     super.appendTo(buffer);
   }
 }
 
 /**
@@ skipping 2194 matching lines @@
 }
 
 /**
  * The interface `FieldElement` defines the behavior of elements representing a field defined
  * within a type.
  */
 abstract class FieldElement implements ClassMemberElement,
     PropertyInducingElement {
   /**
    * Return {@code true} if this element is an enum constant.
-   * 
+   *
    * @return {@code true} if this an enum constant
    */
   bool get isEnumConstant;
 }
 
 /**
  * Instances of the class `FieldElementImpl` implement a `FieldElement`.
  */
 class FieldElementImpl extends PropertyInducingElementImpl implements
     FieldElement {
@@ skipping 7724 matching lines @@
     // bottom <: void (as bottom is a subtype of all types).
     // void <: dynamic (as dynamic is a supertype of all types)
     return identical(type, this) || type.isDynamic;
   }
 
   @override
   VoidTypeImpl substitute2(List<DartType> argumentTypes,
       List<DartType> parameterTypes) =>
       this;
 }