Fix deployable nil exception on job controller

When deployable is nil, we gracefully take care of the case.

app/serializers/deployment_entity.rb

@@ -23,7 +23,7 @@ class DeploymentEntity < Grape::Entity
   expose :last?
   expose :deployed_by, as: :user, using: UserEntity
 
-  expose :deployable do |deployment, opts|
+  expose :deployable, if: -> (deployment) { deployment.deployable.present? } do |deployment, opts|
     deployment.deployable.yield_self do |deployable|
       if include_details?
         JobEntity.represent(deployable, opts)

changelogs/unreleased/fix-nil-deployable-exception-on-job-controller-show.yml

+---
+title: Fix users cannot access job detail page when deployable does not exist
+merge_request: 32247
+author:
+type: fixed

spec/features/projects/jobs_spec.rb

@@ -609,6 +609,14 @@ describe 'Jobs', :clean_gitlab_redis_shared_state do
           expect(find('.js-environment-link')['href']).to match("environments/#{environment.id}")
           expect(find('.js-job-deployment-link')['href']).to include(second_deployment.deployable.project.path, second_deployment.deployable_id.to_s)
         end
+
+        context 'when deployment does not have a deployable' do
+          let!(:second_deployment) { create(:deployment, :success, environment: environment, deployable: nil) }
+
+          it 'has an empty href' do
+            expect(find('.js-job-deployment-link')['href']).to be_empty
+          end
+        end
       end
 
       context 'job failed to deploy' do

spec/serializers/deployment_entity_spec.rb

@@ -36,6 +36,15 @@ describe DeploymentEntity do
     expect(subject).to include(:deployed_at)
   end
 
+  context 'when deployable is nil' do
+    let(:entity) { described_class.new(deployment, request: request, deployment_details: false) }
+    let(:deployment) { create(:deployment, deployable: nil, project: project) }
+
+    it 'does not expose deployable entry' do
+      expect(subject).not_to include(:deployable)
+    end
+  end
+
   context 'when the pipeline has another manual action' do
     let(:other_build) { create(:ci_build, :manual, name: 'another deploy', pipeline: pipeline) }
     let!(:other_deployment) { create(:deployment, deployable: other_build) }