500 page shows when press create merge request.

Hi, I'm a new bee about gitlab and I Setup gitlab on ubantu. I create a project and try to create a merge request. But when I press create merge request the 500 page shows up. Anyone suffers from this? How to fix this.

the production.log output are as follow:

Started GET "/Development/ServerTest/merge_requests/new" for 192.168.3.93 at 2018-07-16 17:42:43 +0800
Processing by Projects::MergeRequests::CreationsController#new as HTML
Parameters: {"namespace_id"=>"Development", "project_id"=>"ServerTest"}
Completed 500 Internal Server Error in 122ms (ActiveRecord: 6.7ms | Elasticsearch: 0.0ms)

TypeError (wrong argument type nil (expected String)):
lib/gitlab/metrics/instrumentation.rb:159:in `block in rev_parse'
lib/gitlab/metrics/method_call.rb:36:in `measure'
lib/gitlab/metrics/instrumentation.rb:159:in `rev_parse'
lib/gitlab/git/repository.rb:548:in `rev_parse_target'
lib/gitlab/git/repository.rb:2520:in `sha_from_ref'
lib/gitlab/git/repository.rb:523:in `raw_log'
lib/gitlab/git/repository.rb:512:in `block in log'
lib/gitlab/gitaly_client.rb:287:in `block (2 levels) in migrate'
lib/gitlab/gitaly_client.rb:331:in `allow_n_plus_1_calls'
lib/gitlab/gitaly_client.rb:280:in `block in migrate'
lib/gitlab/metrics/influx_db.rb:103:in `measure'
lib/gitlab/gitaly_client.rb:278:in `migrate'
lib/gitlab/git/repository.rb:1451:in `gitaly_migrate'
lib/gitlab/git/repository.rb:508:in `log'
lib/gitlab/git/commit.rb:41:in `where'
app/models/repository.rb:150:in `commits'
lib/gitlab/metrics/instrumentation.rb:159:in `block in commits'
lib/gitlab/metrics/method_call.rb:36:in `measure'
lib/gitlab/metrics/instrumentation.rb:159:in `commits'
ee/lib/gitlab/authority_analyzer.rb:23:in `involved_users'
ee/lib/gitlab/authority_analyzer.rb:12:in `calculate'
ee/app/controllers/ee/projects/merge_requests/application_controller.rb:14:in `set_suggested_approvers'
ee/app/controllers/ee/projects/merge_requests/creations_controller.rb:11:in `define_new_vars'
app/controllers/projects/merge_requests/creations_controller.rb:17:in `block in new'
lib/gitlab/gitaly_client.rb:331:in `allow_n_plus_1_calls'
app/controllers/projects/merge_requests/creations_controller.rb:16:in `new'
lib/gitlab/i18n.rb:50:in `with_locale'
lib/gitlab/i18n.rb:56:in `with_user_locale'
app/controllers/application_controller.rb:370:in `set_locale'
lib/gitlab/middleware/multipart.rb:95:in `call'
lib/gitlab/request_profiler/middleware.rb:14:in `call'
ee/lib/gitlab/jira/middleware.rb:15:in `call'
lib/gitlab/middleware/go.rb:17:in `call'
lib/gitlab/etag_caching/middleware.rb:11:in `call'
lib/gitlab/middleware/rails_queue_duration.rb:22:in `call'
lib/gitlab/metrics/rack_middleware.rb:15:in `block in call'
lib/gitlab/metrics/transaction.rb:53:in `run'
lib/gitlab/metrics/rack_middleware.rb:15:in `call'
lib/gitlab/middleware/read_only/controller.rb:28:in `call'
lib/gitlab/middleware/read_only.rb:16:in `call'
lib/gitlab/request_context.rb:18:in `call'
lib/gitlab/metrics/requests_rack_middleware.rb:27:in `call'
lib/gitlab/middleware/release_env.rb:10:in `call'