Comment 5 for bug 1896608

Name: grub-efi/install_devices
Template: grub-efi/install_devices
Value:
Owners: grub-common, grub-efi-amd64
Flags: seen
Variables:
 CHOICES =
 RAW_CHOICES =

Name: grub-efi/install_devices_empty
Template: grub-efi/install_devices_empty
Value: true
Owners: grub-common, grub-efi-amd64
Flags: seen

question is grub-efi/install_devices

  db_get "$question"
  if [ -z "$RET" ]; then
    # Reset the seen flag if the current answer is false, since
    # otherwise we'll loop with no indication of why.
    db_get grub-efi/install_devices_empty
    if [ "$RET" = false ]; then
      db_fset grub-efi/install_devices_empty seen false
    fi
    if db_input critical grub-efi/install_devices_empty; then
      db_go
      db_get grub-efi/install_devices_empty
      if [ "$RET" = true ]; then
        break
      else
        db_fset "$question" seen false
        db_fset grub-efi/install_devices_empty seen false
      fi
    else
      exit 1 # noninteractive
    fi
  else
    break
  fi

So, if install_devices is empty & install_devices_empty is true and seen, asking grub-efi/install_devices_empty will be skipped. and shouldn't error out.

I wonder if I cause this mistake in postinst, and grub-multi-install.