Allow to close invalid merge request

app/models/commit.rb

@@ -150,13 +150,11 @@ class Commit
   end
   def hook_attrs(with_changed_files: false)
-    path_with_namespace = project.path_with_namespace
-
     data = {
       id: id,
       message: safe_message,
       timestamp: committed_date.xmlschema,
-      url: "#{Gitlab.config.gitlab.url}/#{path_with_namespace}/commit/#{id}",
+      url: commit_url,
       author: {
         name: author_name,
         email: author_email
@@ -170,6 +168,10 @@ class Commit
     data
   end
+  def commit_url
+    project.present? ? "#{Gitlab.config.gitlab.url}/#{project.path_with_namespace}/commit/#{id}" : ""
+  end
+
   # Discover issues should be closed when this commit is pushed to a project's
   # default branch.
   def closes_issues(current_user = self.committer)

app/models/merge_request.rb

@@ -213,6 +213,8 @@ class MergeRequest < ActiveRecord::Base
   end
   def validate_branches
+    return if allow_broken
+
     if target_project == source_project && target_branch == source_branch
       errors.add :branch_conflict, "You can not use same project/branch for source and target"
     end
@@ -344,9 +346,12 @@ class MergeRequest < ActiveRecord::Base
   end
   def hook_attrs
+    source_hook_attrs = source_project.hook_attrs if source_project.present?
+    target_hook_attrs = target_project.hook_attrs if target_project.present?
+
     attrs = {
-      source: source_project.hook_attrs,
-      target: target_project.hook_attrs,
+      source: source_hook_attrs,
+      target: target_hook_attrs,
       last_commit: nil,
       work_in_progress: work_in_progress?
     }

spec/controllers/projects/merge_requests_controller_spec.rb

@@ -157,6 +157,35 @@ describe Projects::MergeRequestsController do
     end
   end
+  describe 'PUT #update' do
+    context 'there is no source project' do
+      let(:project) { create(:project) }
+      let(:fork_project) { create(:forked_project_with_submodules) }
+      let(:merge_request) { create(:merge_request_with_diffs, source_project: fork_project, source_branch: 'add-submodule-version-bump', target_branch: 'master', target_project: project) }
+
+      before do
+        fork_project.build_forked_project_link(forked_to_project_id: fork_project.id, forked_from_project_id: project.id)
+        fork_project.save
+        merge_request.reload
+      end
+
+      it 'closes MR without errors' do
+        fork_project.destroy
+
+        post :update,
+            namespace_id: project.namespace.path,
+            project_id: project.path,
+            id: merge_request.iid,
+            merge_request: {
+              state_event: 'close'
+            }
+
+        expect(response).to redirect_to([merge_request.target_project.namespace.becomes(Namespace), merge_request.target_project, merge_request])
+        expect(merge_request.reload.closed?).to be_truthy
+      end
+    end
+  end
+
   describe "DELETE #destroy" do
     it "denies access to users unless they're admin or project owner" do
       delete :destroy, namespace_id: project.namespace.path, project_id: project.path, id: merge_request.iid