substitute crashes with empty replacement rule

Question

This is a bit pathological, but calling substitute with an empty set of rules causes the kernel to crash.

ex := A+B;
substitute(ex, $ $);

or

ex := A+B;
substitute(ex, ${ }$);

This is perhaps more a feature request than a bug report, as it might be nicer if we received the usual error message (i.e. "not a replacement rule or equality").

Answer 1

Now fixed, thanks.