code: def _is_duplicate_file(db_session, filename, hashes):
      
  
      file_ = (
          db_session.query(File)
          .filter(
              (File.filename == filename)
              | (File.blake2_256_digest == hashes["blake2_256"])
          )
          .first()
      )
  
      if file_ is not None:
          return (
              file_.filename == filename
              and file_.sha256_digest == hashes["sha256"]
              and file_.md5_digest == hashes["md5"]
              and file_.blake2_256_digest == hashes["blake2_256"]
          )
  
      return None
docs: Check to see if file already exists, and if it's content matches.
      A file is considered to exist if its filename *or* blake2 digest are
      present in a file row in the database.
  
      Returns:
      - True: This file is a duplicate and all further processing should halt.
      - False: This file exists, but it is not a duplicate.
      - None: This file does not exist.