/// Parses a JSON encoded `null`
/// @param {String} $source - JSON complete source
/// @param {Number} $pointer - current pointer
/// @throw "Unexpected token `n`."
/// @return {List} (new pointer, null)
/// @require {function} _throw
@function _json-decode--null($source, $pointer) {
  $length: str-length($source);

  @if $length - $pointer < 2
  or str-slice($source, $pointer, $pointer) != 'u'
  or str-slice($source, $pointer + 1, $pointer + 1) != 'l'
  or str-slice($source, $pointer + 2, $pointer + 2) != 'l' {
    @return _throw("Unexpected token: `n`.", $pointer);
  }

  @return ($pointer + 3, null);
}