Fixed default value when "type" is an array of types.

Note: The expected default value should match the first type in the types array.

Return whatever's in "default" instead of returning null for everything.
Example:
```javascript
{
    "type": "object",
    "properties": {
        "myProp": {
            "type": ["integer", "string"],
            "default": 5
        }
    }
}
```