def _get_app_revision(environ=None):
if environ is None:<EOL><INDENT>environ = os.environ<EOL><DEDENT>if '<STR_LIT>' in environ:<EOL><INDENT>return environ['<STR_LIT>'].split('<STR_LIT:.>')[<NUM_LIT:1>]<EOL><DEDENT>
Gets the app revision (minor app version) of the current app.

    Args:
      environ: A dictionary with a key CURRENT_VERSION_ID that maps to a version
        string of the format <major>.<minor>.

    Returns:
      The app revision (minor version) of the current app, or None if one couldn't
      be found.