code: public static void put(String key, String val) throws IllegalArgumentException {
          if (key == null) {
              throw new IllegalArgumentException("key parameter cannot be null");
          }
          if (mdcAdapter == null) {
              throw new IllegalStateException("MDCAdapter cannot be null. See also " + NULL_MDCA_URL);
          }
          mdcAdapter.put(key, val);
      }
docs: Put a diagnostic context value (the <code>val</code> parameter) as identified with the
  <code>key</code> parameter into the current thread's diagnostic context map. The
  <code>key</code> parameter cannot be null. The <code>val</code> parameter
  can be null only if the underlying implementation supports it.
  
  <p>
  This method delegates all work to the MDC of the underlying logging system.
  
  @param key non-null key
  @param val value to put in the map
  
  @throws IllegalArgumentException
  in case the "key" parameter is null