I've got some test suites i'm working on that rely on secret keys with no passphrase set. compare the following:
gpg --pinentry-mode=loopback --passphrase='' --quick-gen-key 'test user <email@example.com>'
gpg --pinentry-mode loopback --passphrase '' --quick-gen-key 'test user <firstname.lastname@example.org>'
the latter works as expected, but the former fails with:
gpg: missing argument for option "--passphrase="
It's not clear why an empty string is acceptable as an independent element in argv but is not acceptable as a suffix to a --passphrase= element in argv.
This is particularly aggravating for anyone writing tests or scripts in languages where passing an empty argument as an independent string is more complicated. for example, in simple POSIX shell, a common pattern is to accumulate a list of arguments to hand off to gpg in a single environment variable as a whitespace-delimited string.