BUG #14036: xmin is null in pg_relication_slots

The following bug has been logged on the website:

Bug reference:      14036
Logged by:          Jamie Koceniak
Email address:      jkoceniak@mediamath.com
PostgreSQL version: 9.4.6
Operating system:   Debian
Description:

We just configured 6 replication slots and I noticed that 2 of the 6
replication slots have a NULL value for xmin. Is this problematic?

postgres=# select slot_name, xmin from pg_replication_slots;
   slot_name    |    xmin
----------------+------------
 standb5 | 1571582845
 standby3 | 1571582849
 standby6 | 1571582850
 standby4 | 1571582853
 standby2 |
 standby1 |