code: def occurrence(self, file_name=None, path=None, date=None):
          
          if self._indicator_data.get('type') != 'File':
              # Indicator object has no logger to output warning
              return None
  
          occurrence_obj = FileOccurrence(file_name, path, date)
          self._occurrences.append(occurrence_obj)
          return occurrence_obj
docs: Add a file Occurrence.
  
          Args:
              file_name (str, optional): The file name for this occurrence.
              path (str, optional): The file path for this occurrence.
              date (str, optional): The datetime expression for this occurrence.
  
          Returns:
              obj: An instance of Occurrence.