geraintluff/tv4 — pull request #175 by noirbizarre (2014-12-27 05:15:15+00:00)
Title: Handle undefined properties

This pull-request allow to validate objects with properties set to ``undefined`` if the properties are not required.

It seems coherent with this:
```javascript
JSON.stringify({nullProp: null, undefinedProp: undefined})
>> {"nullProp":null}"
```
So with this schema:
```javascript
var schema = {
properties: {
key: {type: 'string'}
}
};
```
we should have:
```javascript
tv4.validate({key: undefined}, schema);
>> true
tv4.validate({key: null}, schema);
>> false
```