Adds some style changes and fixes a performance issue

app/serializers/diffs_entity.rb

@@ -16,7 +16,7 @@ class DiffsEntity < Grape::Entity
   end
 
   expose :commit do |diffs, options|
-    CommitEntity.represent options[:commit], commit_options(options)
+    CommitEntity.represent(options[:commit], commit_options(options))
   end
 
   expose :context_commits, using: API::Entities::Commit, if: -> (diffs, options) { merge_request&.project&.context_commits_enabled? } do |diffs|
@@ -79,7 +79,7 @@ class DiffsEntity < Grape::Entity
   private
 
   def commit_ids
-    @commit_ids ||= merge_request.commits.collect(&:id)
+    @commit_ids ||= merge_request.recent_commits.map(&:id)
   end
 
   def commit_neighbors(commit_id)

spec/serializers/diffs_entity_spec.rb

@@ -54,7 +54,7 @@ describe DiffsEntity do
         let(:commit) { commits.first }
 
         it 'includes commit references for nil and next' do
-          expect(subject[:commit][:prev_commit_id]).to eq(nil)
+          expect(subject[:commit][:prev_commit_id]).to be_nil
           expect(subject[:commit][:next_commit_id]).to eq(commits.second.id)
         end
       end
@@ -64,7 +64,7 @@ describe DiffsEntity do
 
         it 'includes commit references for previous and nil' do
           expect(subject[:commit][:prev_commit_id]).to eq(commits[-2].id)
-          expect(subject[:commit][:next_commit_id]).to eq(nil)
+          expect(subject[:commit][:next_commit_id]).to be_nil
         end
       end
     end