Use lazy reference extractor to get issue's MRs

app/models/issue.rb

@@ -84,11 +84,11 @@ class Issue < ActiveRecord::Base
   end
 
   def referenced_merge_requests
-    references = [self, *notes].flat_map do |note|
-      note.all_references(load_lazy_references: false).merge_requests
-    end.uniq
-
-    Banzai::LazyReference.load(references).uniq.sort_by(&:iid)
+    Gitlab::ReferenceExtractor.lazily do
+      [self, *notes].flat_map do |note|
+        note.all_references(load_lazy_references: false).merge_requests
+      end
+    end.sort_by(&:iid)
   end
 
   # Reset issue events cache

lib/banzai/reference_extractor.rb

@@ -11,7 +11,7 @@ module Banzai
       end
 
       def lazily(values = nil, &block)
-        return values || block.call if lazy?
+        return (values || block.call).uniq if lazy?
 
         begin
           Thread.current[LAZY_KEY] = true