Check for existing MR only for opened/reopened MR

app/models/merge_request.rb

@@ -92,11 +92,13 @@ class MergeRequest < ActiveRecord::Base
       errors.add :branch_conflict, "You can not use same branch for source and target branches"
     end
 
-    similar_mrs = self.project.merge_requests.where(source_branch: source_branch, target_branch: target_branch).opened
-    similar_mrs = similar_mrs.where('id not in (?)', self.id) if self.id
+    if opened? || reopened?
+      similar_mrs = self.project.merge_requests.where(source_branch: source_branch, target_branch: target_branch).opened
+      similar_mrs = similar_mrs.where('id not in (?)', self.id) if self.id
 
-    if similar_mrs.any?
-      errors.add :base, "There is already an open merge request for this branches"
+      if similar_mrs.any?
+        errors.add :base, "There is already an open merge request for this branches"
+      end
     end
   end