Failed to save children inside the parent node's save callback

[eric-leihe]

Here is my code to create the tree:

`var Bob = new User({ name: 'Bob' });
var Carl = new User({ name: 'Carl' });
Carl.parent = Bob;

Bob.save(function(){
Carl.save(function(){
console.log(Carl);
});
});`

But the inner save of Carl like a blackhole, it never get returned and the console.log never got called.

I dig into the lib/tree.js and finally find that at line 45, "priviousePath" variable is undefined, I think the if condition to enter this block should also check the value of previousPath,
if(isParentChange && previousPath !== undefined ) { // When the parent is changed we must rewrite all children paths as well self.collection.find({ path : { '$regex' : '^' + previousPath + pathSeparator } }, function(err, cursor) { if(err) return next(err);