mybatis/mybatis-3 — pull request #19 by fengxx (2013-03-17 16:31:11+00:00)
Title: Fix NullPoint exception caused by missing TypeHandler

Nested results were handled differently, a resultMap can run in simple query but not in netsted map, e.g.
```xml

select 'ID:'||order_id ref_id ,product_id
from orderDetail
order by product_id

select 'ID:'||order_id ref_id from orderDetail

```

getSimpleResult can run successfully but getProducts will throw null point exception.

The fix added null checking in createRowKeyForMappedProperties method and fall back to resultColumnCache.getTypeHandler if no type handler found.