code: def require_data(self):
          
          files = task.source_missing(self.target)
          if files:
              raise DatacatsError('Missing files in source directory:\n' +
                                  '\n'.join(files))
          if not self.data_exists():
              raise DatacatsError('Environment datadir missing. '
                                  'Try "datacats init".')
          if not self.data_complete():
              raise DatacatsError('Environment datadir damaged or volumes '
                                  'missing. '
                                  'To reset and discard all data use '
                                  '"datacats reset"')
docs: raise a DatacatsError if the datadir or volumes are missing or damaged