Stop query returning all results on 0=0 when using $X{IN} in multi select input controls

[jasperUser12]

I have some cascading input controls setup on my report. Data is customer specific and the 'master' control they can use is restricted based on their login. If we call the main control master1 and the two slave controls slave1 and slave2, slave1 and slave2 are populated based on the value of master1. If I deselect the value in master1 then the $X{IN, column, master1} control evaluates to {0=} (true) and the WHERE filtering is useless and all results are returned.

Is it possible to invert this behaviour and make it so a null value in master1 means nothing is populated in slave1 and slave2?

master1	slave1	slave2
A	john	utah
A	steven	iowa
B	frank	ohio
B	kelly	new york

So if A is selected in master1 then slave1 has choices of john and steven and slave2 has choices of utah and iowa. Similar for master2 being B - slave1/slave2 = frank and kelly/ohio and new york. If I don't select A or B in master1 then slave1 and slave2 have all available choices so john,steven,frank,kelly and utah,iowa,ohio,new york.

All inputs are multi select checkboxes and java.util.Collection types.