anchor.diff:            location);
       }
       _recordImportElementReferenceWithoutPrefix(name);
  -    return super.visitMethodInvocation(node);
  -  }
  -
  -  @override
  -  Object visitPartDirective(PartDirective node) {
  +    super.visitMethodInvocation(node);
  +  }
  +
  +  @override
  +  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) {
  +    super.visitPartDirective(node);
  +  }
  +
  +  @override
  +  visitPartOfDirective(PartOfDirective node) {
       Location location = _createLocationForNode(node.libraryName);
       recordRelationship(node.element, IndexConstants.IS_REFERENCED_BY, location);
  -    return null;
  -  }
  -
  -  @override
  -  Object visitPostfixExpression(PostfixExpression node) {
  +  }
  +
  +  @override
  +  visitPostfixExpression(PostfixExpression node) {
       _recordOperatorReference(node.operator, node.bestElement);
  -    return super.visitPostfixExpression(node);
  -  }
  -
  -  @override
  -  Object visitPrefixExpression(PrefixExpression node) {
  +    super.visitPostfixExpression(node);
  +  }
  +
  +  @override
  +  visitPrefixExpression(PrefixExpression node) {
       _recordOperatorReference(node.operator, node.bestElement);
  -    return super.visitPrefixExpression(node);
  -  }
  -
  -  @override
  -  Object
  -      visitRedirectingConstructorInvocation(RedirectingConstructorInvocation node) {
  +    super.visitPrefixExpression(node);
  +  }
  +
  +  @override
  +  visitRedirectingConstructorInvocation(RedirectingConstructorInvocation node) {
       ConstructorElement element = node.staticElement;
       Location location;
       if (node.constructorName != null) {
  
positive.code:           }
          }
        }
        return super.visitClassTypeAlias(node);
      } finally {
        _exitScope();
      }
    }
  
    @override
    Object visitCompilationUnit(CompilationUnit node) {
      CompilationUnitElement unitElement = node.element;
      if (unitElement != null) {
        _elementStack.add(unitElement);
        _libraryElement = unitElement.enclosingElement;
        if (_libraryElement != null) {
          return super.visitCompilationUnit(node);
        }
      }
      return null;
    }
  
    @override
    Object visitConstructorDeclaration(ConstructorDeclaration node) {
      ConstructorElement element = node.element;
      enterScope(element);
      try {
        return super.visitConstructorDeclaration(node);
      } finally {
        _exitScope();
      }
  
negative.code:   }
  
    @override
    visitConstructorName(ConstructorName node) {
      ConstructorElement element = node.staticElement;
      // in 'class B = A;' actually A constructors are invoked
      if (element != null &&
  