message: assert that there is a device
diff: @@ -4,7 +4,7 @@ import { Volume } from "../component";
  import { optionsFromArguments } from "../core/util/Defaults";
  import { Param } from "../core/context/Param";
  import { readOnly } from "../core/util/Interface";
  -import { isDefined, isNumber } from "../core/util/TypeCheck";
  +import { isDefined, isNumber, isUndef } from "../core/util/TypeCheck";
  export interface UserMediaOptions extends ToneAudioNodeOptions {
  volume: Decibels;
  @@ -109,9 +109,8 @@ export class UserMedia extends ToneAudioNode<UserMediaOptions> {
  // didn't find a matching device
  if (!this._device && devices.length > 0) {
  this._device = devices[0];
  - } else if (!this._device && isDefined(labelOrId)) {
  - throw new Error("UserMedia: no matching device: "+labelOrId);
  }
  + this.assert(isDefined(this._device), `No matching device ${labelOrId}`);
  }
  // do getUserMedia
  let constraints = {
  