[Direct Binary Access] Initiate upload should return null if feature is disabled

Documentation at [0] and implementations disagree with Javadoc [1] for initiateBinaryUpload() regarding determining if the feature is enabled. At [0] it indicates that either a null return value or empty list of upload URIs indicates the feature is disabled, but [1] indicates only a null return value to indicate the feature is disabled.

[0] - https://jackrabbit.apache.org/oak/docs/features/direct-binary-access.html
[1] - https://jackrabbit.apache.org/oak/docs/apidocs/org/apache/jackrabbit/api/JackrabbitValueFactory.html#initiateBinaryUpload-long-int-