Add tests for passing nil values in epics and packages

In https://gitlab.com/gitlab-org/gitlab/-/issues/215936, we found that
upgrading to Grape v1.3.2 caused a regression in our QA suite because
passing a `nil` value for an Array type would be passed in as a `nil`
value instead of being coerced to an empty Array. We had to revert the
upgrade as a result. To ensure that `nil` values are handled properly on
the backend, add tests for this.

ee/spec/requests/api/dependencies_spec.rb

@@ -38,6 +38,17 @@ describe API::Dependencies do
         expect(vulnerability['severity']).to eq('unknown')
       end
 
+      context 'with nil package_manager' do
+        let(:params) { { package_manager: nil } }
+
+        it 'returns no dependencies' do
+          expect(response).to have_gitlab_http_status(:ok)
+          expect(response).to match_response_schema('public_api/v4/dependencies', dir: 'ee')
+
+          expect(json_response).to eq([])
+        end
+      end
+
       context 'with filter options' do
         let(:params) { { package_manager: 'yarn' } }
 

ee/spec/requests/api/epics_spec.rb

@@ -618,6 +618,17 @@ describe API::Epics do
         expect(json_response['labels']).to include '&'
         expect(json_response['labels']).to include '?'
       end
+
+      it 'creates a new epic with no labels' do
+        params[:labels] = nil
+
+        post api(url, user), params: params
+
+        expect(response).to have_gitlab_http_status(:created)
+        expect(json_response['title']).to include 'new epic'
+        expect(json_response['description']).to include 'epic description'
+        expect(json_response['labels']).to be_empty
+      end
     end
   end
 
@@ -705,6 +716,25 @@ describe API::Epics do
           end
         end
 
+        it 'clears labels when labels param is nil' do
+          params[:labels] = 'label1'
+          put api(url, user), params: params
+
+          expect(response).to have_gitlab_http_status(:ok)
+          expect(json_response['title']).to include 'new title'
+          expect(json_response['description']).to include 'new description'
+          expect(json_response['labels']).to contain_exactly('label1')
+
+          params[:labels] = nil
+          put api(url, user), params: params
+
+          expect(response).to have_gitlab_http_status(:ok)
+          json_response = Gitlab::Json.parse(response.body)
+          expect(json_response['title']).to include 'new title'
+          expect(json_response['description']).to include 'new description'
+          expect(json_response['labels']).to be_empty
+        end
+
         it 'updates the epic with labels param as array' do
           stub_const("Gitlab::QueryLimiting::Transaction::THRESHOLD", 110)