code: public boolean isNull(int index) throws LazyException{
  		LazyNode token=getValueToken(index);
  		if(token.type==LazyNode.VALUE_NULL)return true;
  		return false;
  	}
docs: Returns true if the value stored at the given index is null.
  
  @param index the location of the value in this array
  @return true if the value is null, false otherwise
  @throws LazyException if the index is out of bounds