<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_session_user(session_id, **kwargs):
 """ Given a session ID, get the user ID that it is associated with args: session_id (string):
 The user's ID to identify the cookie to remove returns: user_id (string) or None if the session does not exist """


    hydra_session_object = session.SessionObject({}, #This is normally a request object, but in this case is empty
            validate_key=config.get('COOKIES', 'VALIDATE_KEY', 'YxaDbzUUSo08b+'),
            type='file',
            cookie_expires=True,
            data_dir=config.get('COOKIES', 'DATA_DIR', '/tmp'),
            file_dir=config.get('COOKIES', 'FILE_DIR', '/tmp/auth'))

    hydra_session = hydra_session_object.get_by_id(session_id)

    if hydra_session is not None:
        return hydra_session['user_id']

    return None