Fixes #2544 - Can't remove auto assignment timeout.

app/assets/javascripts/app/controllers/_application_controller/form.coffee

@@ -510,7 +510,7 @@ class App.ControllerForm extends App.Controller
           value = false
       if item.type is 'integer'
         if value is ''
-          value = undefined
+          value = null
         else
           value = parseInt(value)
       if param[item.name] isnt undefined

spec/system/manage/groups_spec.rb

@@ -7,4 +7,22 @@
   context 'ajax pagination' do
     include_examples 'pagination', model: :group, klass: Group, path: 'manage/groups'
   end
+
+  context "Issue 2544 - Can't remove auto assignment timeout" do
+    before do
+      visit '/#manage/groups'
+    end
+
+    it 'is possible to reset the assignment timeout of a group' do
+      find('td', text: 'Users').click
+      fill_in 'Assignment Timeout', with: '30'
+      find('button', text: 'Submit').click
+      expect(Group.find_by(name: 'Users').assignment_timeout).to eq(30)
+
+      find('td', text: 'Users').click
+      fill_in 'Assignment Timeout', with: ''
+      find('button', text: 'Submit').click
+      expect(Group.find_by(name: 'Users').assignment_timeout).to be nil
+    end
+  end
 end