Why is ChromeDevtools undefined?

Question

JavaScript

The question is very noob
Why does the interpreter display undefined on the next line after declaring variables:

I tried to declare a variable and set a value for it, after pressing Enter, undefined popped up
After that I decided to declare a variable, but do not put anything there to check, the answer is also undefined
It seemed to me that in in the first case, nothing should be displayed, and the second variable should be NULL
Or is NULL only needed to explicitly indicate that there was never anything in the variable?