Description:
------------
http://php.net/manual/en/class.mongoid.php

def: public __construct ([ string $id = NULL ] )

any string!

why new MongoId ('-1'); // generate exception?
but new MongoId ('5197647495931abe07000000');

pecl version of mongo 1.4.0. on 1.3.X branch it was ok

Test script:
---------------
<?
$id = MongoId ('-1');

Expected result:
----------------
get_type($id ) => MongoId instance

Actual result:
--------------
exception:
object(MongoException)[41]
  protected 'message' => string 'Invalid object ID' (length=17)
  private 'string' (Exception) => string '' (length=0)
  protected 'code' => int 19
  protected 'file' => ...