Returns a null-friendly comparator that considers
null to be
less than non-null. When both are
null, they are considered
equal. If both are non-null, the specified
Comparator is used
to determine the order. If the specified comparator is
then the returned comparator considers all non-null values to be equal.
The returned comparator is serializable if the specified comparator is serializable.
|the type of the elements to be compared|
| a |
null to be less than
non-null, and compares non-null objects with the supplied