public Map<String, String> getCopyOfContextMap() {
        Map<String, String> oldMap = inheritableThreadLocalMap.get();
        if (oldMap != null) {
            return new HashMap<>(oldMap);
        } else {
            return null;
        }
    }
Return a copy of the current thread's context map.
Returned value may be null.
slf4j-api/src/main/java/org/slf4j/helpers/BasicMDCAdapter.java