code: private void fileNameInput(List<FileModel> vertices, GraphRewrite event, ParameterStore store)
      {
          if (this.filenamePattern != null)
          {
              Pattern filenameRegex = filenamePattern.getCompiledPattern(store);
              //in case the filename is the first operation generating result, we can use the graph regex index. That's why we distinguish that in this clause
              if (vertices.isEmpty() && StringUtils.isBlank(getInputVariablesName()))
              {
                  FileService fileService = new FileService(event.getGraphContext());
                  for (FileModel fileModel : fileService.findByFilenameRegex(filenameRegex.pattern()))
                  {
                      vertices.add(fileModel);
                  }
              }
              else
              {
                  ListIterator<FileModel> fileModelIterator = vertices.listIterator();
                  vertices.removeIf(fileModel -> !filenameRegex.matcher(fileModel.getFileName()).matches());
              }
          }
      }
docs: Generating the input vertices is quite complex. Therefore there are multiple methods that handles the input vertices based on the attribute
  specified in specific order. This method handles the {@link FileContent#inFileNamed(String)} attribute.