Programming :: Null Pointer In Bash?

#!/bin/bash
sed -n 8p file.txt

returns the 8th line to the StdOut.

If I assign the value to the variable line = $(sed -n 8p file.txt)

and now print it out with echo

echo $line

the line would be printed.

But what if the file has only 4 lines. What value would be assigned to the variable line?

I want to know that because I want to only print it if the value is "something", that is not null.

In Java for example I would do it like this...
String line = "";
line = reader.readLine(); // or anything else..
if(line!=null){
System.out.println(line);
}

How would I check if the value is not "null"(I don't know if bash knows null)