Glad to report that it doesn't fail in the CheckVariablesFilter, but I also tried this:
```
module TEST
  rule .K => ?A ~> !A
endmodule
```
 and I got the following error message:
```
[Warning] Compiler: Module K-FRESH undefined.
        File: D:\work\k\include\modules\substitution.k
        Location: (8,3,8,17)
        Compilation Phase: class
org.kframework.compile.FlattenModules$FlattenModulesVisitor
```
@andreistefanescu any idea why?