anchor.diff:            IndexConstants.IS_WRITTEN_BY :
             IndexConstants.IS_REFERENCED_BY;
         _store.recordRelationship(element.field, relationship, location);
  -      return null;
  +      return;
       }
       // record specific relations
       if (element is ClassElement ||
  
positive.code:           location);
      }
      _recordImportElementReferenceWithoutPrefix(name);
      return super.visitMethodInvocation(node);
    }
  
    @override
    Object visitPartDirective(PartDirective node) {
      Element element = node.element;
      Location location = _createLocationForNode(node.uri);
      recordRelationship(element, IndexConstants.IS_REFERENCED_BY, location);
      return super.visitPartDirective(node);
    }
  
    @override
    Object visitPartOfDirective(PartOfDirective node) {
      Location location = _createLocationForNode(node.libraryName);
      recordRelationship(node.element, IndexConstants.IS_REFERENCED_BY, location);
      return null;
    }
  
    @override
    Object visitPostfixExpression(PostfixExpression node) {
      _recordOperatorReference(node.operator, node.bestElement);
      return super.visitPostfixExpression(node);
    }
  
    @override
    Object visitPrefixExpression(PrefixExpression node) {
      _recordOperatorReference(node.operator, node.bestElement);
      return super.visitPrefixExpression(node);
    }
  
    @override
    Object
        visitRedirectingConstructorInvocation(RedirectingConstructorInvocation node) {
      ConstructorElement element = node.staticElement;
      Location location;
      if (node.constructorName != null) {
  
negative.code:           }
          }
        }
        super.visitClassTypeAlias(node);
      } finally {
        _exitScope();
      }
    }
  
    @override
    visitCompilationUnit(CompilationUnit node) {
      CompilationUnitElement unitElement = node.element;
      if (unitElement != null) {
        _elementStack.add(unitElement);
        _libraryElement = unitElement.enclosingElement;
        if (_libraryElement != null) {
          super.visitCompilationUnit(node);
        }
      }
    }
  
    @override
    visitConstructorDeclaration(ConstructorDeclaration node) {
      ConstructorElement element = node.element;
      enterScope(element);
      try {
        super.visitConstructorDeclaration(node);
      } finally {
        _exitScope();
      }
  