BABYLON.DigitalRainPostProcess is not a constructor

I am trying to make a scene like its raining. But I have been facing this error . I dont know what is causing it . I copy the same as the documentation.

Hey! Do not forget to reference the postprocesses library:

<script src="https://cdn.babylonjs.com/postProcessesLibrary/babylonjs.postProcess.min.js"></script>