MessageBufferInput.next()

[xerial]

Based on the discussion in #82 (diff), we determined the behavior of MessageBufferInput.next() as follows:

MessageBufferInput.next() returns null if there're no more buffers. Unpacker throws MessageDataInsufficientException (which extends MessagePackException) if more data is necessary to unpack a value.

[xerial]

InsufficientDataException will be added when supporting event-driven I/O #92.

For now no action is required for this issue.