After upgrade to gitlab-10.5.6-ee

How to Use GitLab
1

After updating gitlab-10.5.3-ee to gitlab-10.5.6-ee in the docker when running the webhook test, I get the error 500
In logs:

Started GET "/eurosoft/ebb_new/hooks/23/test?trigger=merge_requests_events" for 10.42.76.125 at 2018-03-21 09:10:18 +0000
Processing by Projects::HooksController#test as HTML
  Parameters: {"trigger"=>"merge_requests_events", "namespace_id"=>"eurosoft", "project_id"=>"ebb_new", "id"=>"23"}
Completed 500 Internal Server Error in 156ms (ActiveRecord: 15.3ms | Elasticsearch: 0.0ms)

URI::InvalidURIError (URI::InvalidURIError):
  lib/gitlab/proxy_http_connection_adapter.rb:14:in `connection'
  app/services/web_hook_service.rb:73:in `make_request'
  app/services/web_hook_service.rb:26:in `execute'
  app/models/hooks/web_hook.rb:10:in `execute'
  app/services/test_hooks/base_service.rb:22:in `block in execute'
  app/services/test_hooks/base_service.rb:19:in `catch'
  app/services/test_hooks/base_service.rb:19:in `execute'
  app/controllers/projects/hooks_controller.rb:41:in `test'
  lib/gitlab/i18n.rb:47:in `with_locale'
  lib/gitlab/i18n.rb:53:in `with_user_locale'
  app/controllers/application_controller.rb:333:in `set_locale'
  lib/gitlab/middleware/multipart.rb:95:in `call'
  lib/gitlab/request_profiler/middleware.rb:14:in `call'
  lib/gitlab/middleware/go.rb:17:in `call'
  lib/gitlab/etag_caching/middleware.rb:11:in `call'
  lib/gitlab/middleware/read_only.rb:31:in `call'
  lib/gitlab/request_context.rb:18:in `call'
  lib/gitlab/metrics/requests_rack_middleware.rb:27:in `call'
2

I think you need to enable outbound request in your gitlab, read the post about the latest release, https://about.gitlab.com/2018/03/20/critical-security-release-gitlab-10-dot-5-dot-6-released/