Comment 19 for bug 1692127

This also works for me on xenial with apport version 2.20.1-0ubuntu2.9:

== DuplicateSignature =================================
package:linux-image-4.4.0-84-generic:4.4.0-84.107
Setting up linux-image-4.4.0-84-generic (4.4.0-84.107) ...
Running depmod.
update-initramfs: deferring update (hook will be called later)
Examining /etc/kernel/postinst.d.
run-parts: executing /etc/kernel/postinst.d/apt-auto-removal 4.4.0-84-generic /boot/vmlinuz-4.4.0-84-generic
run-parts: executing /etc/kernel/postinst.d/initramfs-tools 4.4.0-84-generic /boot/vmlinuz-4.4.0-84-generic
update-initramfs: Generating /boot/initrd.img-4.4.0-84-generic
run-parts: executing /etc/kernel/postinst.d/pm-utils 4.4.0-84-generic /boot/vmlinuz-4.4.0-84-generic
run-parts: executing /etc/kernel/postinst.d/unattended-upgrades 4.4.0-84-generic /boot/vmlinuz-4.4.0-84-generic
run-parts: executing /etc/kernel/postinst.d/update-notifier 4.4.0-84-generic /boot/vmlinuz-4.4.0-84-generic
run-parts: executing /etc/kernel/postinst.d/zz-update-grub 4.4.0-84-generic /boot/vmlinuz-4.4.0-84-generic
/usr/sbin/grub-mkconfig: 15: /etc/default/grub: Syntax error: Unterminated quoted string
run-parts: /etc/kernel/postinst.d/zz-update-grub exited with return code 2
Failed to process /etc/kernel/postinst.d at /var/lib/dpkg/info/linux-image-4.4.0-84-generic.postinst line 1052.
dpkg: error processing package linux-image-4.4.0-84-generic (--configure):
 subprocess installed post-installation script returned error exit status 2