Changes to nullable type returning

For all get* functions on InputDataGetter classes, there is now a slightly modified behavior. Apart from with getString, if the input data contains an empty string, it is represented by null, rather than the default for that type.

This means that if there is a number input on the page, and the user does not enter any data into it, calling getInt() on that field will now return null instead of 0 - properly representing an absence of data, without making any assumptions.

This is a minor release, due to minor backwards breaking changes.