Check outstanding RPC is not null

Before it receives the handling of the command.
The outstanding RPC can be null in case of async call.

Fix TTL test

Merge branch 'rabbitmq-java-client-104' into stable

Merge branch 'rabbitmq-java-client-104' into stable

Makefile: Generate javadoc in `make dist`

Allow for higher delivery latency for CI containers

Fix a few Javadoc warnings

[#127354185]

Fix a few Javadoc warnings

[#127354185]

Merge pull request rabbitmq#159 from rabbitmq/license-headers

Update license / copyright headers