Export gpg secret key without passphrase

In gpg 1.4.16 I can gpg --export-secret-keys <key> without a passphrase, and it isn't a problem. However, I cannot find anyway to do this in v2.1.9. It asks if I am okay with no passphase, I confirm, and it skips the key. There must be some configuration option to have it do as I please. What is it?

Do you need a passphrase for GPG key?

To help safeguard your key, GnuPG does not store your raw private key on disk. Instead it encrypts it using a symmetric encryption algorithm. That is why you need a passphrase to access the key.

For anyone still being hit by this problem (like me): It was a regression in gpg versions beginning at 2.1.0 which was fixed in 2.1.13.

See discussion and fix.