imapsync: Can't use an undefined value as a HASH reference

Hi,

I'm trying to sync a large mailbox with imapsync, but imapsync exits with this error:

Can't use an undefined value as a HASH reference at /usr/local/bin/imapsync line 12643.

Anyone has an idea whats going wrong here or how to fix this?

I found this thread without a solution: https://community.grommunio.com/d/1010-grommunio-imapsync-hash-error/2

Thanks