Expose commit author's gravatar if not gitlab user

app/serializers/commit_entity.rb

@@ -3,6 +3,10 @@ class CommitEntity < API::Entities::RepoCommit
 
   expose :author, using: UserEntity
 
+  expose :author_gravatar_url do |commit|
+    GravatarService.new.execute(commit.author_email)
+  end
+
   expose :commit_url do |commit|
     namespace_project_tree_url(
       request.project.namespace,

spec/serializers/commit_entity_spec.rb

@@ -41,4 +41,8 @@ describe CommitEntity do
 
     subject
   end
+
+  it 'exposes gravatar url that belongs to author' do
+    expect(subject.fetch(:author_gravatar_url)).to match /gravatar/
+  end
 end