For Case Management, the combination of async + autostart raises an exception

A NPE exception is raised [1] when the combination of async mode and autostart is set to an ad-hoc task.

This should either be fixed in the code to not have an error, or have the designer's UIs prevent from checking both options in the corresponding checkboxes.

[1] 

2023-12-02 06:53:03,274 ERROR [org.jbpm.runtime.manager.impl.error.ExecutionErrorHandlerImpl] (EE-ManagedThreadFactory-default-Thread-1) Unexpected error during processing : java.lang.NullPointerException

2023-12-02 06:53:03,275 WARN  [org.jbpm.executor.impl.AbstractAvailableJobsExecutor] (EE-ManagedThreadFactory-default-Thread-1) Error during command org.jbpm.process.core.async.AsyncSignalEventCommand error message null: java.lang.NullPointerException