docs: @Override
      public FileModel resolvePayload(GraphRewrite event, EvaluationContext context, WindupVertexFrame payload)
      {
          checkVariableName(event, context);
          if (payload instanceof FileReferenceModel)
          {
              return ((FileReferenceModel) payload).getFile();
          }
          if (payload instanceof FileModel)
          {
              return (FileModel) payload;
          }
          return null;
      }