[Rails 5] build_details_entity_spec.rb - undefined method `to_sym' for nil:NilClass

https://gitlab.com/gitlab-org/gitlab-ce/-/jobs/71422042

 1) BuildDetailsEntity#as_json contains the needed key value pairs
     Failure/Error: CALLOUT_FAILURE_MESSAGES[failure_reason.to_sym]

     NoMethodError:
       undefined method `to_sym' for nil:NilClass
       Did you mean?  to_s
     # ./app/presenters/commit_status_presenter.rb:14:in `callout_failure_message'
     # ./app/serializers/job_entity.rb:61:in `callout_message'
     # ./spec/serializers/build_details_entity_spec.rb:24:in `block (3 levels) in <top (required)>'
     # ./spec/serializers/build_details_entity_spec.rb:31:in `block (3 levels) in <top (required)>'