How to specify an array as a formal argument type in structured search

I'm trying to find all the places in my code where a null is passwd as a parameter where the argument type is an array:

void foo(Integer [] bar) {}
...
foo(null);

I used the unboxing template as a starting point and was able to find all of the places where a null is passed as a parameter, but everytime I try to put a regular expression matching an array declaration into the slot for the 'formal argument type of the method' it fails to find any cases. (I'm using a dummy file where I know that there is the above case)

I've tried

\[\]
\w\s\[\]
Integer \[\] bar


etc...