If you inadvertently delete the /dev/null link, you can recreate it by using the devlinks command. The null device is basically a bit bucket. Here's an example.
# cd /dev/
# ls -l null
null: No such file or directory
# devlinks
# ls -l null
lrwxrwxrwx 1 root other 27 Aug 10 16:11 null -> ../devices/pseudo
mm@0:null
If null device and link is missing, use mknod.
# cd /devices/pseudo
# mknod mm@0:null c 13 2
# chown root:sys mm@0:null
# chmod 666 mm@0:null
# devlinks