 	 * @param  {String | Number} key
 	###
 	release = (obj, key) ->
-		obj[key] = undefined
+		obj[key] = $nil
 		return
 
 	###*

	$circularChain = 'promise_circular_chain'

	$invalid_argument = 'invalid_argument'

	# Default state
	_state: $pending

		p._state = state
		p._value = value

		if state == $rejected
			if isLongStackTrace and value and value.stack
				stack = genStackInfo value, p
				value.stack = stack[0] + stack[1]

			if not p._pre or p._pre._state == $resolved
				scheduleUnhandledRejection p

		i = 0
		len = p._pCount
