Upload API throws RuntimeException

Hello,

You should provide an easy way to handle upload errors in your SDK.

The method signature suggests that you will be throwing an IOException but looking at the source code, we can see that you're actually throwing RuntimeException in several cases ! These cases should be handled differently in the SDK so that the caller can identify them : they are definitely not a reason to throw a RuntimeException.

At the minimum, you should throw a IOException as specified by the upload signature.
Alternatively, you could think about a nicer error handling system, either with a custom Exception or with a specific Map returned (whose values should be documented !).