ux: fix bug where saving empty issue tracker form was causing

exception, fixes:  #4278

rhodecode/controllers/admin/settings.py

@@ -397,19 +397,20 b' class SettingsController(BaseController)'
         settings_model = IssueTrackerSettingsModel()
 
         form = IssueTrackerPatternsForm()().to_python(request.POST)
-        for uid in form['delete_patterns']:
-            settings_model.delete_entries(uid)
+        if form:
+            for uid in form.get('delete_patterns', []):
+                settings_model.delete_entries(uid)
 
-        for pattern in form['patterns']:
-            for setting, value, type_ in pattern:
-                sett = settings_model.create_or_update_setting(
-                    setting, value, type_)
-                Session().add(sett)
+            for pattern in form.get('patterns', []):
+                for setting, value, type_ in pattern:
+                    sett = settings_model.create_or_update_setting(
+                        setting, value, type_)
+                    Session().add(sett)
 
-            Session().commit()
+                Session().commit()
 
-        SettingsModel().invalidate_settings_cache()
-        h.flash(_('Updated issue tracker entries'), category='success')
+            SettingsModel().invalidate_settings_cache()
+            h.flash(_('Updated issue tracker entries'), category='success')
         return redirect(url('admin_settings_issuetracker'))
 
     @HasPermissionAllDecorator('hg.admin')

rhodecode/tests/functional/test_admin_settings.py

@@ -494,6 +494,14 b' class TestAdminSettingsIssueTracker:'
         response = self.app.get(url('admin_settings_issuetracker'))
         assert response.status_code == 200
 
+    def test_add_empty_issuetracker_pattern(
+            self, request, autologin_user, csrf_token):
+        post_url = url('admin_settings_issuetracker_save')
+        post_data = {
+            'csrf_token': csrf_token
+        }
+        self.app.post(post_url, post_data, status=302)
+
     def test_add_issuetracker_pattern(
             self, request, autologin_user, csrf_token):
         pattern = 'issuetracker_pat'