message: don't try to set an undefined attribute
diff: @@ -152,8 +152,8 @@ export abstract class ToneWithContext<Options extends ToneWithContextOptions> ex
  */
  set(props: Partial<Options>): this {
  Object.keys(props).forEach(attribute => {
  - if (Reflect.has(this, attribute)) {
  - if (isDefined(this[attribute]) && isDefined(this[attribute].value)) {
  + if (Reflect.has(this, attribute) && isDefined(this[attribute])) {
  + if (isDefined(this[attribute].value)) {
  this[attribute].value = props[attribute];
  } else if (this[attribute] instanceof ToneWithContext) {
  this[attribute].set(props[attribute]);
  