I noticed that there is no null folder in dev
Because you are looking at the partition while the system is not running.
/dev contains device nodes created by the kernel, mostly during boot. They are not real files in the sense of being a sequence of bytes stored somewhere, which is why they usually appear to be of 0 size.
When the system is not running,
/dev should be empty. When it is running, a special file system of type
devtmpfs is mounted there. It is unmounted at shutdown or will otherwise cease to exist if the system stops since it exists only in memory.
Should I create it?
No. Anything put into
/dev when the system is down will be hidden under the mount point anyway. Also,
/dev/null, as implied, is not a normal file.