NullPointerException on Shutdown without Start

[nils-christian]

Hi,

We noticed an interesting behaviour of (at least) the MessageHandlerRegistrar which fails with a NPE when it is stopped but not started.

Basic information

• Axon Framework version: 4.6.2
• JDK version: 11
• Complete executable reproducer if available (e.g. GitHub Repo):

final Configuration configuration = DefaultConfigurer
		.defaultConfiguration( )
		.registerQueryHandler( c -> new Object( ) )
		.buildConfiguration( );
configuration.shutdown( );

Steps to reproduce

Please take a look at the above code.

Expected behaviour

The shutdown should - in my opinion - never fail with a NPE, even if it has never been started. Either make sure that the components can handle this (no exception at all) or make sure that shutdown can not be called without being started first (IllegalStateException with clear message).

Actual behaviour

The shutdown fails with a NullPointerException in MessageHandlerRegistrar.

[smcvb]

Definitely a caveat, but a good catch regardless.
Luckily the fix is easy as well.

I do notice that the Configuration#shutdown will swallow the exception into a warning log statement.
It does so to keep shutting down, instead of breaking the system mid-shutdown.
Nonetheless, the exception is unhelpful noise that should not be generated.

[smcvb]

And I created a PR for it.

[smcvb]

Closing this issue, since it's resolved in pull request #2482.