VirtualMachine.provisioningState() should return Enum

As of today, VirtualMachine.provisioningState() returns a String and I am unable to find what String values it could return. By trail and error, we found a few interesting states but seems that is not the most reliable way to produce stable code.
Please make this to return an Enum and please document the meaning of each State.

Documentation: https://azure.github.io/azure-sdk-for-java/com/microsoft/azure/management/compute/VirtualMachine.html#provisioningState--

I can understand that the underlying REST API is only returning a String instead of providing a list of possible values. Probably this is not simply a problem of the JAVA SDK. As a customer, I would hope you could take this feedback to the Azure REST API team and make the improvement together.
https://docs.microsoft.com/en-us/rest/api/compute/virtualmachines/get

For a short term, at least have better documentation on what are the possible values. Else, how do you expect a customer to use this API?

Thanks