Minor Description
If a consumer sends a disposition with Modified state in which the 'deliveryFailed' field is not populated, the broker will NPE. This is because the relevant value is a Boolean object rather than boolean primitive. That appears to be because there is actually no default value specified for the field in the specification, and it is defined only to be set when delivery actually failed (values that are not set are encoded nulls in the AMQP frame).
The implementation needs updated to handle this value being null, but will be left permissive of it being set false.