Use Class.new(StandardError) instead of custom extended error class. Bring back…

app/models/ci/build.rb

@@ -6,6 +6,8 @@ module Ci
     include Presentable
     include Importable
 
+    MissingDependenciesError = Class.new(StandardError)
+
     belongs_to :runner
     belongs_to :trigger_request
     belongs_to :erased_by, class_name: 'User'
@@ -141,8 +143,8 @@ module Ci
       end
 
       before_transition any => [:running] do |build|
-        if !build.empty_dependencies? && build.dependencies.empty?
-          raise Gitlab::Ci::Error::MissingDependencies
+        if build.specified_dependencies? && build.dependencies.empty?
+          raise MissingDependenciesError
         end
       end
     end
@@ -484,6 +486,10 @@ module Ci
       options[:dependencies]&.empty?
     end
 
+    def specified_dependencies?
+      options.has_key?(:dependencies) && options[:dependencies].any?
+    end
+
     def hide_secrets(trace)
       return unless trace
 

app/services/ci/register_job_service.rb

@@ -54,7 +54,7 @@ module Ci
           # we still have to return 409 in the end,
           # to make sure that this is properly handled by runner.
           valid = false
-        rescue Gitlab::Ci::Error::MissingDependencies
+        rescue Ci::Build::MissingDependenciesError
           build.drop!(:missing_dependency_failure)
           valid = false
         end

lib/gitlab/ci/error/missing_dependencies.rb

-module Gitlab
-  module Ci
-    module Error
-      class MissingDependencies < StandardError; end
-    end
-  end
-end

spec/lib/gitlab/ci/error/missing_dependencies_spec.rb

-require 'spec_helper'
-
-describe Gitlab::Ci::Error::MissingDependencies do
-  it { expect(described_class).to be < StandardError }
-end

spec/models/ci/build_spec.rb

@@ -1893,7 +1893,7 @@ describe Ci::Build do
       end
 
       context 'when depended jobs do not exist' do
-        it { expect { build.run! }.to raise_error(Gitlab::Ci::Error::MissingDependencies) }
+        it { expect { build.run! }.to raise_error(Ci::Build::MissingDependenciesError) }
       end
     end
   end