Null AuthData causes kernel panic during LDAP sync

Environment

• Mattermost Server: 5.25.2

Steps to Reproduce

1. Configure LDAP sync and have some users set up to return a null value for the AuthData value. (Setting the LDAP IdAttribute to objectGUID can cause this)
2. Do an LDAP sync in a cluster

Expected Behavior

Sync is successful, cluster operates normally, null users show an error in LDAP sync report

Observed Behavior

The null value causes a nil pointer dereference panic for all servers in the cluster:

Users with these ObjectGUIDs had a null value in their AuthData. Manually adding them resolved the issue:

• \f6\d3\ff\6e\f1\35\fd\49\a1\31\7c\59\e4\85\b7\c9

• \72\83\bd\54\3a\d3\01\49\9d\89\72\7b\90\53\27\c0

• \30\60\2c\44\d7\f4\03\49\9e\a2\c8\aa\54\77\97\ab

• \56\0c\d7\45\d1\ef\67\4e\81\c4\bc\ec\43\1c\71\69

• \3f\a8\ce\60\73\48\fe\45\a1\6c\c7\4b\db\56\79\e8

• \22\42\1b\d9\a4\2d\02\47\83\0d\14\69\ec\a0\ec\04

• \24\ab\ae\0e\f0\13\3d\44\aa\43\67\2f\cd\0b\0c\27

• \af\3f\f1\64\2a\ba\7f\4e\83\db\12\12\87\72\44\6e

• \7e\6a\2a\ec\e8\72\99\46\bd\93\9d\d6\50\9e\04\84

• \af\34\16\4a\4f\8a\a8\4c\81\96\0d\c6\b8\ef\01\d3

• \0d\93\b9\34\f2\a5\28\47\b9\39\13\60\ea\21\38\87

• \6c\72\1e\52\c2\cc\bf\44\99\8d\bd\a9\e5\14\0c\65