If you are using a Nightly release, try upgrading to a version higher than hrev59825 as there was a change introduced in that version that added audio over HDMI/DP support to the HDA driver that caused issues with existing HD Audio devices.
Audio actually still works but if you have a video card with audio support over the HDMI/DP port in your system it seems default to that upon updating and you need to switch to your normal HD Audio device in Media preferences. It also overrode the output/input mixer settings for all devices with the HDMI/DP one, showing HDMI <NULL> due to limitations of the HDA driver.
It was reverted in hrev59826. I logged a ticket about it as I experienced issues with it, link to the ticket here: Making sure you're not a bot!
