code: protected function getValue($event)
      {
          if ($this->value === null) {
              $request = Yii::$app->getRequest();
              $lock = $this->getLockAttribute();
              $formName = $this->owner->formName();
              $formValue = $formName ? ArrayHelper::getValue($request->getBodyParams(), $formName . '.' . $lock) : null;
              $input = $formValue ?: $request->getBodyParam($lock);
              $isValid = $input && (new NumberValidator())->validate($input);
              return $isValid ? $input : 0;
          }
  
          return parent::getValue($event);
      }
docs: {@inheritdoc}
  
  In case of `null`, value will be parsed from [[\yii\web\Request::getBodyParam()|getBodyParam()]] or set to 0.