I don't have a RAID but get the warning mdadm.conf defines no arrays

I installed 16.04 Server and I have had a similar message in my logs and this message when I upgrade initramfs packages through normal package upgrade.

...
Setting up initramfs-tools (0.122ubuntu8.3) ...
update-initramfs: deferring update (trigger activated)
Processing triggers for initramfs-tools (0.122ubuntu8.3) ...
update-initramfs: Generating /boot/initrd.img-4.4.0-38-generic
W: mdadm: /etc/mdadm/mdadm.conf defines no arrays.

Is this normal, or is Ubuntu expecting to find a RAID because of some misconfiguration somewhere?

Here is the contents of /etc/mdadm/mdadm.conf:

# mdadm.conf
#
# Please refer to mdadm.conf(5) for information about this file.
#

# by default (built-in), scan all partitions (/proc/partitions) and all
# containers for MD superblocks. alternatively, specify devices to scan, using
# wildcards if desired.
#DEVICE partitions containers

# auto-create devices with Debian standard permissions
CREATE owner=root group=disk mode=0660 auto=yes

# automatically tag new arrays as belonging to the local system
HOMEHOST <system>

# instruct the monitoring daemon where to send mail alerts
MAILADDR root

# definitions of existing MD arrays

The error says W: mdadm: /etc/mdadm/mdadm.conf defines no arrays.

I reckon that the warning is displayed whenever there's no ARRAY line in mdadm.conf.

The obvious solution would be to add one:

ARRAY <ignore> devices=/dev/sda

Worked for me...