Extend error checking to be overwritten in EE

app/services/merge_requests/merge_base_service.rb

@@ -8,6 +8,10 @@ class MergeBaseService < MergeRequests::BaseService
 
     attr_reader :merge_request
 
+    # Overridden in EE.
+    def error_check!
+    end
+
     # Overridden in EE.
     def hooks_validation_pass?(_merge_request)
       true

app/services/merge_requests/merge_service.rb

@@ -46,6 +46,8 @@ def authorization_check!
     end
 
     def error_check!
+      super
+
       error =
         if @merge_request.should_be_rebased?
           'Only fast-forward merge is allowed for your project. Please update your source branch'

app/services/merge_requests/merge_to_ref_service.rb

@@ -33,6 +33,8 @@ def validate!
     end
 
     def error_check!
+      super
+
       error =
         if Feature.disabled?(:merge_to_tmp_merge_ref_path, project)
           'Feature is not enabled'