code: @Override
  	public int compare(final T o1, final T o2) {
  		int result = 0;
  		if (o1 == null) {
  			if (o2 != null) {
  				result = -1;
  			}
  		} else if (o2 == null) {
  			result = 1;
  		} else {
  			result = compareType(o1, o2);
  		}
  		return result;
  	}
docs: Compares two objects null safe to each other.
  
  @param o1
  the first reference
  @param o2
  the second reference
  @return a negative value if o1 < o2, zero if o1 = o2 and a positive value if o1 > o2