code: public boolean isNull(String key){
  		LazyNode token=getOptionalFieldToken(key);
  		if(token==null)return true;
  		if(token.type==LazyNode.VALUE_NULL)return true;
  		return false;
  	}
docs: Returns true if the value stored in this object for the given key is null.
  
  @param key the name of the field on this object
  @return true if the value is null, false otherwise
  @throws LazyException if no value was set for the given key.