getFiltersString on FreeformQueryDelegate's implementation

Hi all!

In the Book of Vaadin, on chapter 14.7, at the end of it, is presented a demo implementation of FreeformStatementDelegate in:
I’ve grabbed this java class and made the necessary modifications to the new package/class structure of Vaadin 6.7.1

But there’s something missing. I can’t find an implementation of the method toWhereString() of the class Filter.
I need this to write getFiltersString() on an implementation of FreeformQueryDelegate.

If anyone can point-me to a (current) implementation of FreeformQueryDelegate, i’ll appreciate a lot.

Thanks in advance,
David Pinheiro