Improved PropsSplitter to handle missing fields
Improved PropsSplitter to handle missing fields

* Use PropVal::atOrNone instead of operator[]
* Set output to default if conversion from None is not defined for
  output type

aguetlein/databricxx,databricxx/databricxx,aguetlein/databricxx,oschulz/databricxx,oschulz/databricxx,databricxx/databricxx