Set packet data/optional default value in create()

[the01]

Calling the Packet.create() method causes the logger to emit warnings about using default values for Packet.data and Packet.optional when instantiating the new packet.
This uses the default value [] explicitly to stop the warnings.

[coveralls]

Coverage remained the same at 91.316% when pulling a800ced on the01:master into 38d1852 on kipe:master.

[kipe]

Thanks, looks good 👍