Is there any option to make the output 'null' to empty?

I love this simple tool, but I found out a problem here.
In shell script, the `null` value matches the string check inconvenient since `[ -z $var ]` is usually for checking empty string and the `null` string makes it failed. The solution here is that we need to remove the `null` string becoming a empty string.
I think maybe `jp` could add a option to solve this problem as it's really common for writing shell script.
Thanks!