assertCalculation method Null safety

SassCalculation assertCalculation(
  1. [String? name]
)

Throws a SassScriptException if this isn't a calculation.

If this came from a function argument, name is the argument name (without the $). It's used for error reporting.

Implementation

SassCalculation assertCalculation([String? name]) =>
    throw _exception("$this is not a calculation.", name);