在React App中升级到Webpack 4时出现错误。我试图在Internet上找到解决方案，但是这个问题不存在。
Uncaught TypeError: Cannot set property 'reactAlertEvents' of undefined
at new AlertContainer (alert.js?5001:528)
at eval (ReactCompositeComponent.js?888e:294)
at measureLifeCyclePerf (ReactCompositeComponent.js?888e:75)
at ReactCompositeComponentWrapper._constructComponentWithoutOwner (ReactCompositeComponent.js?888e:293)
at ReactCompositeComponentWrapper._constructComponent (ReactCompositeComponent.js?888e:284)
at ReactCompositeComponentWrapper.mountComponent (ReactCompositeComponent.js?888e:187)
at Object.mountComponent (ReactReconciler.js?37a8:43)
at ReactDOMComponent.mountChildren (ReactMultiChild.js?0cbd:234)
at ReactDOMComponent._createInitialChildren (ReactDOMComponent.js?17ad:703)
at ReactDOMComponent.mountComponent (ReactDOMComponent.js?17ad:522)