Using Kleopatra

Try using Kleopatra, a graphical certificate manager.

• Select the relevant keypair
• Right-click Change passphrase
• in the popup window leave the field blank (i.e. using an empty password as the current one)
• in the subsequent popup enter the new password and confirm it.

Using pinentry

Also, you could try this solution which uses the pinentry utility.

these are three possible solutions, please let us know if/any one works in your case.

Please note: I didn't have the chance to try any of these (I have no empty-password gpg keyring), but researched and searched through the man pages/webpages!

Using passphrase-fd

--passphrase-fd in conjunction with --batch allows you to enter an empty string through the pipe:

echo '' | gpg2 --batch --passphrase-fd 0 your other options 

Using Kleopatra

Try using Kleopatra, a graphical certificate manager.

• Select the relevant keypair
• Right-click Change passphrase
• in the popup window leave the field blank (i.e. using an empty password as the current one)
• in the subsequent popup enter the new password and confirm it.

Using pinentry

Also, you could try this solution which leverages the pinentry utility.