Now handles objects with null-valued properties or fields.

When inserting, it ignores properties/fields.
When updating, it deletes the properties/fields.

As per https://www.dropbox.com/developers/blog/56/how-the-dropbox-datastore-api-handles-conflicts-part-two-resolving-collisions:

    Field Deletions

    Another detail I glossed over is how field deletions are handled. There are different schools of thought about these. Some consider a field deletion a special operation, which should always win in case of a field-field conflict. This is what the SDK currently does, but there are certain problems with this approach. Fortunately we haven't heard from anyone running into those problems.

    Others prefer to think of it as equivalent to setting the value to null, and resolving conflicts using the standard basic algorithm for two field updates. it is likely that we will change the SDK to use this approach. (The effect of a field deletion on the snapshot will not change — after a field is deleted, the field is deemed no longer to exist.)