<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_access_token(self):
 """Method to return the current requests' access_token. :returns: Access token or None :rtype: str .. versionadded:: 1.2 """

        try:
            credentials = OAuth2Credentials.from_json(
                self.credentials_store[g.oidc_id_token['sub']])
            return credentials.access_token
        except KeyError:
            logger.debug("Expired ID token, credentials missing",
                         exc_info=True)
            return None