(module
  (func (export "externref") (result externref) (ref.null extern))
  (func (export "exnref") (result exnref) (ref.null exn))
  (func (export "funcref") (result funcref) (ref.null func))

  (global externref (ref.null extern))
  (global exnref (ref.null exn))
  (global funcref (ref.null func))
)

(assert_return (invoke "externref") (ref.null extern))
(assert_return (invoke "exnref") (ref.null exn))
(assert_return (invoke "funcref") (ref.null func))