code: @Override
      public Object put(ChronoElement<?> key, Object value) {
  
          Object obj = super.put(key, value);
  
          if (
              (key == null)
              || (obj == null)
              || obj.equals(value)
          ) {
              return obj;
          } else {
              throw new AmbivalentValueException(key);
          }
  
      }
docs: ~ Methoden ----------------------------------------------------------