Bug 1129660 - Adding users to user group throws Internal server error.
Description: 389-ds-base-1.2.11 branch did not have the commit
a71633d56951dd6c4d0368c790b85628f1598968 (Ticket #47313 - Indexed
search with filter containing '&' and "!" with attribute subtypes
gives wrong result).
This patch backporting just the NULL idl checking in idl_common.c
from the commit to the 389-ds-base-1.2.11 branch.
Reviewed by firstname.lastname@example.org (Thank you, Nathan!!)
(cherry picked from commit 488fa1229f0f0b80cbe43f2e52c2e2b3aaefe188)