0.2.3

ensure additionalData is empty object instead of array

Also ensured the interface's method signature to be kept by defaulting additionalData to null instead of [].
When json encoding, we check whether additionalData is an empty array and if it is, we pass a stdClass (generic empty class in PHP) instead of the empty array to fix the issue of empty arrays being passed to the control center logs

contributes to #PURPLE-249