anchor.diff:          // TODO(a14n): remove this check to have a lot more const widget
           if (children[index] == null) {
             throw FlutterError(
  -              "$runtimeType's children must not contain any null values, "
  -                  'but a null value was found at index $index',
  +            "$runtimeType's children must not contain any null values, "
  +            'but a null value was found at index $index',
             );
           }
         }
  
positive.code:             ErrorSummary('setState() or markNeedsBuild() called during build.'),
              ErrorDescription(
                'This ${widget.runtimeType} widget cannot be marked as needing to build because the framework '
                'is already in the process of building widgets.  A widget can be marked as '
                'needing to be built during the build phase only if one of its ancestors '
                'is currently building. This exception is allowed because the framework '
                'builds parent widgets before children, which means a dirty descendant '
                'will always be built. Otherwise, the framework might not visit this '
                'widget during this build phase.',
              ),
              describeElement(
                'The widget on which setState() or markNeedsBuild() was called was',
              ),
            ];
            if (owner!._debugCurrentBuildTarget != null)
              information.add(owner!._debugCurrentBuildTarget!.describeWidget('The widget which was currently being built when the offending call was made was'));
  
negative.code:               error = FlutterError.fromParts(<DiagnosticsNode>[
                  ErrorSummary('Multiple widgets used the same GlobalKey.'),
                  ErrorDescription(
                    'The key $key was used by multiple widgets. The parents of those widgets were:\n'
                    '- ${older.toString()}\n'
                    '- ${newer.toString()}\n'
                    'A GlobalKey can only be specified on one widget at a time in the widget tree.',
                  ),
                ]);
              } else {
                error = FlutterError.fromParts(<DiagnosticsNode>[
                  ErrorSummary('Multiple widgets used the same GlobalKey.'),
                  ErrorDescription(
                    'The key $key was used by multiple widgets. The parents of those widgets were '
                    'different widgets that both had the following description:\n'
                    '  ${parent.toString()}\n'
                    'A GlobalKey can only be specified on one widget at a time in the widget tree.',
                  ),
                ]);
              }
  