What is the meaning of a question mark in bash variable parameter expansion as in ${var?}?

Question

What is the meaning of a bash variable used like this:

 ${Server?}

Answer 1

:? causes the (non-interactive) shell to exit with an error message if given parameter is null or unset. The script you are looking at is omitting the error message; usually, you'd see something like

foo=${1:?Missing first argument}

For example,

$ foo=${1:?Missing first argument}
bash: 1: Missing first argument
$ set firstarg
$ foo=${1:?Missing first argument}
$ echo $foo
firstarg