Previously, you could only use this when setting the handle afterwards.
* lisp/eshell/esh-io.el (eshell-set-output-handle): Don't catch
'eshell-null-device' here...
(eshell-get-target): ... catch it here.
* test/lisp/eshell/eshell-tests.el
(eshell-test/eshell-command/output-dev-null): New test (bug#72857).