1 files changed, 5 insertions, 1 deletions
diff --git a/lib/gitlab/sql/union.rb b/lib/gitlab/sql/union.rb
index f30c771837a..c99b262f1ca 100644
--- a/lib/gitlab/sql/union.rb
+++ b/lib/gitlab/sql/union.rb
@@ -26,7 +26,11 @@ module Gitlab
           @relations.map { |rel| rel.reorder(nil).to_sql }.reject(&:blank?)
         end
 
-        fragments.join("\n#{union_keyword}\n")
+        if fragments.any?
+          fragments.join("\n#{union_keyword}\n")
+        else
+          'NULL'
+        end
       end
 
       def union_keyword