Thanks! If any user was impacted, they have (at least) a couple options after updating to v4.5.2-2:
- Easy: reboot the router and /dev/null should be back to normal (at least I see that on squashfs)
- Advanced: Delete and re-create the file:
rm /dev/null; mknod -m 666 /dev/null c 1 3
And probably other methods in between.