QEMU crashes with "-global driver=isa-fdc"

QEMU (current master branch at commit 935efca6) aborts when it is run like this:

 qemu-system-x86_64 -global driver=isa-fdc
 qemu-system-x86_64: ../../devel/qemu/qapi/string-input-visitor.c:394:
  string_input_visitor_new: Assertion `str' failed.
 Aborted (core dumped)

Even if the command line is incomplete in that case, QEMU should not abort but rather print a proper error message instead.