Create valid duration object when null is passed to moment.duration()

moment.js

@@ -1998,6 +1998,8 @@
  s: parseIso(match[7]),
  w: parseIso(match[8])
  };
+ } else if (duration == null) {// checks for null or undefined
+ duration = {};
  } else if (typeof duration === 'object' &&
  ('from' in duration || 'to' in duration)) {
  diffRes = momentsDifference(moment(duration.from), moment(duration.to));

test/moment/duration.js

@@ -62,6 +62,18 @@ exports.duration = {
  test.done();
  },
 
+ 'undefined instantiation' : function (test) {
+ test.expect(1);
+ test.equal(moment.duration(undefined).milliseconds(), 0, 'milliseconds');
+ test.done();
+ },
+
+ 'null instantiation' : function (test) {
+ test.expect(1);
+ test.equal(moment.duration(null).milliseconds(), 0, 'milliseconds');
+ test.done();
+ },
+
  'instantiation by type' : function (test) {
  test.expect(16);
  test.equal(moment.duration(1, 'years').years(), 1, 'years');