/// Return a default value if some value is not defined.
///
/// @group helpers_logic
///
/// @parameter {Any} $value   - a value
/// @parameter {Any} $default - the default value to use if `$value` is `null`
///
/// @example scss - Usage
///   k-default($margin, 10px)
@function k-default($value, $default) {
  @return if($value, $value, $default);
}