Ignition Report - Version key is not working as intended

While creating report, added 2 row versions - Standard and Completed
The row versions depends on value of 3 different keys - x,y,z
I added version key like -
(x != NULL && y != NULL && z != NULL)?"Completed":"Standard"
This is not working as intended
When I give some value to x (y and z are NULL), then itself the row is versioned as 'Completed'
Please let me know if I'm providing the expression correctly

The reportmill keychain pdf might be of help here. I see that it says NULL values get evaluated to false and non-null get evaluated to true. So you might try
x && y && z?"Completed":"Standard"