How to check negation in SASS (SCSS)?

Question

Sass

Greetings!
I created a test mixin for demonstration and set a condition for the presence of $arg to it:

@mixin test($arg) {
  @if($arg) {
    @error $arg;
  }
}

If $arg comes in, then the check passes. I'm trying to negate $arg and get a syntax error:

@mixin test($arg) {
  @if(!$arg) {
    @error $arg;
  }
}

How to correctly check negation in SASS (SCSS)?
Thank you!

Answer 1

@mixin test($arg) {
  @if(not $arg) {
    @error $arg;
   }
}