Rule that uses unasserted fact blows up.

[rvanderwall]

I have a rule that fires if a fact exists, so A(X,Y) <= has_fact(X) & other_stuff(X,Y)

If I load up my WME and none of them happen to assert has_fact(), the rule throws an exception. I can get around it by asserting and retracting a dummy rule like this:
+ has_fact('dummy') - has_fact('dummy')