Handle null values in clearTimeout

lib/timers.js

@@ -209,9 +209,11 @@ exports.setTimeout = function (callback, after) {
 
 
 exports.clearTimeout = function (timer) {
-  timer.callback = timer._onTimeout = null;
-  exports.unenroll(timer);
-  if (timer instanceof Timer) timer.stop(); // for after === 0
+  if (timer) {
+    timer.callback = timer._onTimeout = null;
+    exports.unenroll(timer);
+    if (timer instanceof Timer) timer.stop(); // for after === 0
+  }
 };
 
 

test/pummel/test-timers.js

@@ -8,6 +8,10 @@ var WINDOW = 200; // why is does this need to be so big?
 var interval_count = 0;
 var setTimeout_called = false;
 
+// check that these don't blow up.
+clearTimeout(null);
+clearInterval(null);
+
 assert.equal(true, setTimeout instanceof Function);
 var starttime = new Date;
 setTimeout(function () {