private static void emitReplayOrSubstituionWarning(SubstituteLoggingEvent event, int queueSize) {
        if (event.getLogger().isDelegateEventAware()) {
            emitReplayWarning(queueSize);
        } else if (event.getLogger().isDelegateNOP()) {
            // nothing to do
        } else {
            emitSubstitutionWarning();
        }
    }
The value of PROVIDER.getMDCAdapter() can be null while PROVIDER has not yet initialized.

However, SLF4JServiceProvider implementations are expected to initialize their internal
MDCAdapter field in their constructor or on field declaration.
slf4j-api/src/main/java/org/slf4j/LoggerFactory.java