ASSERT failure in qv4ssa.cpp: for(x in y || {})

I wanted to add '|| {}' as a default for a potentially uninitiallized y.
Evaluation of the following two lines then resulted in a crash:

var y = {};
for(var x in y || {}) ;

I'm not sure whether this is valid JavaScript at all. However even when it's not there should be an error instead of an crash.