Fix normalize parameters

Not so fast, man. You won battle, but won't win a war :)

I don't want to see undefined as required parameter (in my opinion it's nonsense). But you can use undefined value anyway.
```javascript
var method = new ApiMethod({
    name : 'method',
    params : { value : {description: 'Can be undefined'}},
    action : function (params) { 
        return params.value === undefined; 
    }
});
method.exec({ value : undefined }); // true
```

> undefined value
> primitive value used when a variable has not been assigned a value

http://www.ecma-international.org/ecma-262/5.1/#sec-4.3.9

> null value
> primitive value that represents the intentional absence of any object value

http://www.ecma-international.org/ecma-262/5.1/#sec-4.3.11

So, if you need to pass absence of value, pass `null` not `undefined`.