private static void emitReplayWarning(int eventCount) {
        Reporter.warn("A number (" + eventCount + ") of logging calls during the initialization phase have been intercepted and are");
        Reporter.warn("now being replayed. These are subject to the filtering rules of the underlying logging system.");
        Reporter.warn("See also " + REPLAY_URL);
    }
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