function literalScale(defaultValue) {
  function scale(d) {
    if (d === undefined) {
      return defaultValue;
    }
    return d;
  }

  function response() {
    return scale;
  }

  scale.domain = response;
  scale.range = response;
  scale.unknown = response;
  scale.copy = response;

  return scale;
}
Return a d3 scale that returns the literal value that was given to it
@returns {function} literal scale.