Some quick refactors to make the pipelines pass

Also makes the code a little more verbose

app/serializers/diffs_entity.rb

@@ -85,16 +85,15 @@ class DiffsEntity < Grape::Entity
     end
   end
 
-  def commits(id)
-    commit_ids.each_cons(3) do |prev_commit, commit, next_commit|
-      { prev_commit_id: prev_commit, next_commit_id: next_commit } if commit == id
-    end
+  def commit_with_neighbors(id)
+    commits = commit_ids.each_cons(3).find { |prev_commit, commit, next_commit| commit == id }
+    { prev_commit_id: commits.first, next_commit_id: commits.last } if commits
   end
 
   def commit_options(options)
-    neighbors = commits(options[:commit].id)
-    prev_commit_id = neighbors.try(:prev_commit_id)
-    next_commit_id = neighbors.try(:next_commit_id)
+    neighbors = commit_with_neighbors(options[:commit]&.id)
+    prev_commit_id = neighbors&.dig(:prev_commit_id)
+    next_commit_id = neighbors&.dig(:next_commit_id)
 
     options.merge(
       type: :full,

spec/serializers/diffs_entity_spec.rb

@@ -28,8 +28,8 @@ describe DiffsEntity do
     end
 
     context "when a commit_id is passed" do
-      let(:commits) { merge_request.commits }
-      let(:commit) { commits.sample }
+      let(:commits) { [nil] + merge_request.commits + [nil] }
+      let(:commit) { commits.compact.sample }
       let(:entity) do
         described_class.new(merge_request_diffs.first.diffs, request: request, merge_request: merge_request, merge_request_diffs: merge_request_diffs, commit: commit)
       end