code: public void addTrace (String info) {
  		if (info == null) throw new IllegalArgumentException("info cannot be null.");
  		if (trace == null) trace = new StringBuffer(512);
  		trace.append('\n');
  		trace.append(info);
  	}
docs: Adds information to the exception message about where in the the object graph serialization failure occurred. Serializers
  can catch {@link JsonException}, add trace information, and rethrow the exception.