def external_system_identifiers(endpoint):
@utils.flatten<EOL>@utils.for_each_value<EOL>def _external_system_identifiers(self, key, value):<EOL><INDENT>new_recid = maybe_int(value.get('<STR_LIT:d>'))<EOL>if new_recid:<EOL><INDENT>self['<STR_LIT>'] = get_record_ref(new_recid, endpoint)<EOL><DEDENT>return [<EOL>{<EOL>'<STR_LIT>': '<STR_LIT>',<EOL>'<STR_LIT:value>': ext_sys_id,<EOL>} for ext_sys_id in force_list(value.get('<STR_LIT:a>'))<EOL>]<EOL><DEDENT>return _external_system_identifiers<EOL>
Populate the ``external_system_identifiers`` key.

    Also populates the ``new_record`` key through side effects.