Misleading error message when user tries to register from not-white-listed email domain

Summary

If email address of a new user that tries to register does not appear neither in white nor in black list, Gitlab CE shows misleading message 'Could not authenticate you from Ldapmain because "Undefined method `provider' for 'nil:nilclass'"'

Steps to reproduce

1. Gitlab CE version 11.10.4 (gitlab-ce@62c464651d2df6f4002af4e4967d11be9aec8d92), installed from Gitlab-Omnibus
2. In general settings, add following settings in "Signup restrictions"
   1. Sign-up enabled: False
   2. Send confirmation email on sign-up: True
   3. Add "*.corp.com" in "Whitelisted domains for sign-ups" (note the dot after an asterisk)
   4. Leave empty "Blacklisted domains for sign-ups"
3. Configure LDAP
4. Try to register a new user, existing in LDAP with email "user@corp.com"

What is the current bug behavior?

User is not allowed to sign-up and is displayed a message above.

application.log nevertheless contains more informative message "Email domain is not authorized for sign-up".

What is the expected correct behavior?

More informative error message should be displayed in browser.

Relevant logs and/or screenshots

Respective log line:

(LDAP) Error saving user cn=username,ou=part,ou=lab,ou=team,ou=srr,dc=corp,dc=net (user@corp.com): ["Email domain is not authorized for sign-up"]

Results of GitLab environment info

Expand for output related to GitLab environment info

System information
System:         Ubuntu 14.04
Current User:   git
Using RVM:      no
Ruby Version:   2.5.3p105
Gem Version:    2.7.6
Bundler Version:1.17.3
Rake Version:   12.3.2
Redis Version:  3.2.12
Git Version:    2.18.1
Sidekiq Version:5.2.5
Go Version:     unknown
GitLab information
Version:        11.10.4
Revision:       62c464651d2
Directory:      /opt/gitlab/embedded/service/gitlab-rails
DB Adapter:     PostgreSQL
DB Version:     9.6.11
URL:            https://internal-server.corp.com
HTTP Clone URL: https://internal-server.corp.com/some-group/some-project.git
SSH Clone URL:  git@internal-server.corp.com:some-group/some-project.git
Using LDAP:     yes
Using Omniauth: no
GitLab Shell
Version:        9.0.0
Repository storage paths:
default:      /mnt/gitlab/repositories
GitLab Shell path:              /opt/gitlab/embedded/service/gitlab-shell
Git:            /opt/gitlab/embedded/bin/git

Results of GitLab application Check

Expand for output related to the GitLab application check

Checking GitLab subtasks ...
Checking GitLab Shell ...
GitLab Shell: ... GitLab Shell version >= 9.0.0 ? ... OK (9.0.0)
Running /opt/gitlab/embedded/service/gitlab-shell/bin/check
Check GitLab API access: OK
Redis available via internal API: OK
Access to /var/opt/gitlab/.ssh/authorized_keys: OK
gitlab-shell self-check successful
Checking GitLab Shell ... Finished
Checking Gitaly ...
Gitaly: ... default ... OK
Checking Gitaly ... Finished
Checking Sidekiq ...
Sidekiq: ... Running? ... yes
Number of Sidekiq processes ... 1
Checking Sidekiq ... Finished
Checking Incoming Email ...
Incoming Email: ... Reply by email is disabled in config/gitlab.yml
Checking Incoming Email ... Finished
Checking LDAP ...
LDAP: ... Server: ldapmain
LDAP authentication... Success
LDAP users with access to your GitLab server (only showing the first 100 results)
DN: cn=restrictedusergroup1,ou=github,ou=mosaic,ou=service accounts,dc=corp,dc=net	 sAMAccountName: $3AI830-0L9KIAJ8QRDL
removed 99 lines
Checking LDAP ... Finished
Checking GitLab App ...
Git configured correctly? ... yes
Database config exists? ... yes
All migrations up? ... yes
Database contains orphaned GroupMembers? ... no
GitLab config exists? ... yes
GitLab config up to date? ... yes
Log directory writable? ... yes
Tmp directory writable? ... yes
Uploads directory exists? ... yes
Uploads directory has correct permissions? ... yes
Uploads directory tmp has correct permissions? ... yes
Init script exists? ... skipped (omnibus-gitlab has no init script)
Init script up-to-date? ... skipped (omnibus-gitlab has no init script)
Projects have namespace: ...
6/2 ... yes
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Redis version >= 2.8.0? ... yes
Ruby version >= 2.5.3 ? ... yes (2.5.3)
Git version >= 2.18.0 ? ... yes (2.18.1)
Git user has default SSH configuration? ... yes
Active users: ... 115
Checking GitLab App ... Finished
Checking GitLab subtasks ... Finished