Finds submission by ID.

    Args:
      submission_id: ID of the submission

    Returns:
      SubmissionDescriptor with information about submission or None if
      submission is not found.

def find_by_id(self, submission_id):
    """Finds submission by ID.

    Args:
      submission_id: ID of the submission

    Returns:
      SubmissionDescriptor with information about submission or None if
      submission is not found.
    """
    return self._attacks.get(
        submission_id,
        self._defenses.get(
            submission_id,
            self._targeted_attacks.get(submission_id, None)))