Major Description
When gc-free logging is used with mixed synchronous/asynchronous loggers, parameter values are replaced with "null" after the first AsyncLoggerConfig.
The message format is still present, as well as the parameter count, however all values are nulls.
It appears that Log4jEventWrapperHandler.onEvent invokes MutableLogEvent.clear, which nulls out the parameter array.
I have constructed a failing test (which I need to clean up and deduplicate some code from the fix for LOG4J2-2299):
https://github.com/cakofony/logging-log4j2/commit/b9c03f5c6881bfe778f8e2d75d046ce6e021c4f1
