code: function () {
  	      if (!specialPropKeyWarningShown) {
  	        specialPropKeyWarningShown = true;
  	        process.env.NODE_ENV !== 'production' ? warning(false, '%s: `key` is not a prop. Trying to access it will result ' + 'in `undefined` being returned. If you need to access the same ' + 'value within the child component, you should pass it as a different ' + 'prop. (https://fb.me/react-special-props)', displayName) : void 0;
  	      }
  	      return undefined;
  	    }
docs: Create dummy `key` and `ref` property to `props` to warn users against its use