Cdn Endpoint Update API cannot update the value of property originPath

I am trying to update the value of property `originPath` to `empty value` with [`Endpoints_Update`](https://github.com/Azure/azure-rest-api-specs/blob/e83bb3392a13e1bb0b2c2cbdf4597d0a0edde49d/specification/cdn/resource-manager/Microsoft.Cdn/stable/2019-04-15/cdn.json#L655). So I set this property value as `""` in http request body but it failed and threw below error message after tested. And I also tried to set it as `nil` in http request body but it still isn't updated to empty value. May I know is it expected?

Error message:
```
cdn.EndpointsClient#Update: Failure sending request: StatusCode=400 -- Original Error: Code="BadRequest" Message="Property 'Endpoint.OriginPath' cannot be set to ''. "
```

Read specification/cdn/resource-manager/Microsoft.Cdn/stable/2019-04-15/cdn.json around line 655 and inspect the Endpoints_Update definition for originPath. Compare that definition with the reported empty-string and nil requests; done means confirming the expected behavior and identifying whether the API specification needs a clearly scoped correction.

Written by the indexing model from the issue text.