Adds a step to the RestWrite#execute chain: it cleans the response
authData object of null values.
For example, this:
{"authData": {"anonymous": null}, "updatedAt", ...}
will be transformed to this:
{"updatedAt", ...}
And this:
{"authData": {"anonymous": null, "twitter": ...}, "updatedAt", ...}
will be transformed to this:
{"authData": {"twitter": ...}, "updatedAt", ...}
Fixing this issue will fix anonymous user upgrades from the Android SDK.
1b8e613dfb