Fall back on ghost user when deploy key user is not set

app/models/deploy_key.rb

@@ -27,6 +27,10 @@ class DeployKey < Key
     self.private?
   end
 
+  def user
+    super || User.ghost
+  end
+
   def has_access_to?(project)
     deploy_keys_project_for(project).present?
   end

lib/gitlab/git_access.rb

@@ -99,8 +99,6 @@ module Gitlab
     end
 
     def check_active_user!
-      return if deploy_key?
-
       if user && !user_access.allowed?
         raise UnauthorizedError, ERROR_MESSAGES[:account_blocked]
       end
@@ -219,7 +217,7 @@ module Gitlab
         raise UnauthorizedError, ERROR_MESSAGES[:read_only]
       end
 
-      if deploy_key
+      if deploy_key?
         unless deploy_key.can_push_to?(project)
           raise UnauthorizedError, ERROR_MESSAGES[:deploy_key_upload]
         end
@@ -309,8 +307,10 @@ module Gitlab
         case actor
         when User
           actor
+        when DeployKey
+          nil
         when Key
-          actor.user unless actor.is_a?(DeployKey)
+          actor.user
         when :ci
           nil
         end

spec/models/deploy_key_spec.rb

@@ -17,4 +17,25 @@ describe DeployKey, :mailer do
       should_not_email(user)
     end
   end
+
+  describe '#user' do
+    let(:deploy_key) { create(:deploy_key) }
+    let(:user) { create(:user) }
+
+    context 'when user is set' do
+      before do
+        deploy_key.user = user
+      end
+
+      it 'returns the user' do
+        expect(deploy_key.user).to be(user)
+      end
+    end
+
+    context 'when user is not set' do
+      it 'returns the ghost user' do
+        expect(deploy_key.user).to eq(User.ghost)
+      end
+    end
+  end
 end