In most contexts empty file is indeed a valid executable. Debian folks learned this the hard way recently:
https://bugs.debian.org/919341
However, executing /dev/null doesn't seem to work on Linux:
$ sudo chmod 777 /dev/null
$ /dev/null
bash: /dev/null: Permission denied
Cf http://trillian.mit.edu/~jc/humor/ATT_Copyright_true.html or https://twitter.com/rob_pike/status/966896123548872705