Make sure that artifacts_file is nullified after removing artifacts

app/models/ci/build.rb

@@ -341,6 +341,7 @@ module Ci
     def erase_artifacts!
       remove_artifacts_file!
       remove_artifacts_metadata!
+      save
     end
 
     def erase(opts = {})

spec/workers/expire_build_artifacts_worker_spec.rb

@@ -20,6 +20,10 @@ describe ExpireBuildArtifactsWorker do
       it 'does remove files' do
         expect(build.reload.artifacts_file.exists?).to be_falsey
       end
+
+      it 'does nullify artifacts_file column' do
+        expect(build.reload.artifacts_file_identifier).to be_nil
+      end
     end
 
     context 'with not yet expired artifacts' do
@@ -32,6 +36,10 @@ describe ExpireBuildArtifactsWorker do
       it 'does not remove files' do
         expect(build.reload.artifacts_file.exists?).to be_truthy
       end
+
+      it 'does not nullify artifacts_file column' do
+        expect(build.reload.artifacts_file_identifier).not_to be_nil
+      end
     end
 
     context 'without expire date' do
@@ -44,6 +52,10 @@ describe ExpireBuildArtifactsWorker do
       it 'does not remove files' do
         expect(build.reload.artifacts_file.exists?).to be_truthy
       end
+
+      it 'does not nullify artifacts_file column' do
+        expect(build.reload.artifacts_file_identifier).not_to be_nil
+      end
     end
 
     context 'for expired artifacts' do