public void setContextMap(Map<String, String> contextMap) {
        Map<String, String> copy = null;
        if (contextMap != null) {
            copy = new HashMap<>(contextMap);
        }
        inheritableThreadLocalMap.set(copy);
    }
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