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grub2-mkconfig produces this output line on my machine:
linux   /vmlinuz-4.1.15-8-default root=UUID=  splash=silent quiet showopts

This way the system simply cannot boot, and systemd waits forever on the root
filesystem device.

Reproducible: Always

Steps to Reproduce:
1. Unsure what specific system configuration leads to this, been running this
system for months without issues.
2. run grub2-mkconfig
3. examine output
Actual Results:  
a look at /etc/grub.d/10_linux revealed that:
GRUB_DEVICE=/dev/sda3 # thats just fine
GRUB_DEVICE_UUID="" # So apparently grub2 cannot find out the uuid of my root
filesystem.
Line 53 is executed and puts no uuid as root= on the cmdline

Sidenote: GRUB_DISABLE_LINUX_UUID feature in /etc/default/grub is broken too

Expected Results:  
I would expect grub2 to fallback to /dev/sda3 if it can not find an UUID, to
make sure something still works. Sadly it does not.

just from looking at /etc/grub.d/10_linux:50 I can tell that grub2 will never
fall back to the non-uuid device path, unless / is on LVM. This doesn't look
right to me.

Some system details:
NAME                    MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
sda                       8:0    0    42G  0 disk  
������sda1                    8:1    0     1M  0 part  
������sda2                    8:2    0     1G  0 part  /boot
������sda3                    8:3    0  36,9G  0 part  /
������sda4                    8:4    0     4G  0 part  [SWAP]
and then many more disks where I got /home on LVM on raid1 with 3 disks
/boot: ext4
/: f2fs