After upgrade to 3.x get an error on "power management" page.

Failed to index key 'powerbtn' of 'powerbtn.0' because it has no children.
Error #0: exception 'RuntimeException' with message 'Failed to index key 'powerbtn' of 'powerbtn.0' because it has no children.' in /usr/share/php/openmediavault/dictionary.inc:145 Stack trace: #0 /usr/share/php/openmediavault/config/configobject.inc(193): OMV\Dictionary->set('powerbtn.0', '1') #1 /usr/share/php/openmediavault/config/configobject.inc(271): OMV\Config\ConfigObject->set('powerbtn.0', '1', false) #2 /usr/share/php/openmediavault/config/configobject.inc(233): OMV\Config\ConfigObject->setFlatAssoc(Array, false, false) #3 /usr/share/php/openmediavault/config/database.inc(90): OMV\Config\ConfigObject->setAssoc(Array, false) #4 /usr/share/php/openmediavault/config/database.inc(96): OMV\Config\Database->get('conf.system.pow...', NULL) #5 /usr/share/openmediavault/engined/rpc/powermgmt.inc(56): OMV\Config\Database->getAssoc('conf.system.pow...') #6 [internal function]: OMVRpcServicePowerMgmt->get(NULL, Array) #7 /usr/share/php/openmediavault/rpc/serviceabstract.inc(124): call_user_func_array(Array, Array) #8 /usr/share/php/openmediavault/rpc/rpc.inc(86): OMV\Rpc\ServiceAbstract->callMethod('get', NULL, Array) #9 /usr/sbin/omv-engined(536): OMV\Rpc\Rpc::call('PowerMgmt', 'get', NULL, Array, 1) #10 {main}

omv-showkey powermanagement
    <powermanagement>
      <cpufreq>1</cpufreq>
      <powerbtn>1</powerbtn>
      <powerbtn>shutdown</powerbtn>
    </powermanagement>