ListCommitByOid isn't called with an empty batch

Batching commits for performance improvements, might lead to empty
batches being used. This isn't the case yet, but to guard against this
in future cases, a guard clause is added.

lib/gitlab/gitaly_client/commit_service.rb

@@ -179,6 +179,8 @@ module Gitlab
       end
       def list_commits_by_oid(oids)
+        return [] if oids.empty?
+
         request = Gitaly::ListCommitsByOidRequest.new(repository: @gitaly_repo, oid: oids)
         response = GitalyClient.call(@repository.storage, :commit_service, :list_commits_by_oid, request, timeout: GitalyClient.medium_timeout)

spec/lib/gitlab/git/commit_spec.rb

@@ -421,6 +421,16 @@ describe Gitlab::Git::Commit, seed_helper: true do
       end
     end
+    describe '#batch_by_oid' do
+      context 'when oids is empty' do
+        it 'makes no Gitaly request' do
+          expect(Gitlab::GitalyClient).not_to receive(:call)
+
+          described_class.batch_by_oid(repository, [])
+        end
+      end
+    end
+
     shared_examples 'extracting commit signature' do
       context 'when the commit is signed' do
         let(:commit_id) { '0b4bc9a49b562e85de7cc9e834518ea6828729b9' }