@abstractmethod<EOL><INDENT>def release_run_as(self):<DEDENT>
pass<EOL>
This method releases the current 'run as' (assumed) identity and reverts
to the previous 'pre run as' identity that existed before run_as was called.

This method returns 'run as' (assumed) identity being released or None
if this Subject is not operating under an assumed identity.

:returns: the 'run as' (assumed) identity being released or None if this
          Subject is not operating under an assumed identity