message must be optional and default to ""

index.bs

@@ -5372,8 +5372,9 @@ shape for developers. Specifically:
  of the names in the [=error names table=].
 * The [=interface=] must have a [=constructor operation=] which sets the instance's
  [=DOMException/name=] to the interface's [=identifier=].
-* Their [=constructor operation=] must take as its first parameter a {{DOMString}} named |message|,
- and must set the instance's [=DOMException/message=] to |message|.
+* Their [=constructor operation=] must take as its first parameter an [=optional=] {{DOMString}}
+ named |message| defaulting to the empty string, and must set the instance's
+ [=DOMException/message=] to |message|.
 * Their [=constructor operation=] should take as its second parameter a [=dictionary=] containing
  the additional information that needs to be exposed.
 * They should have [=read only=] [=attributes=], whose names are the same as the members of the
@@ -5392,7 +5393,7 @@ interfaces will always return 0.
  <pre highlight=webidl>
  [Exposed=Window]
  interface WidgetError : DOMException {
- constructor(DOMString message, WidgetErrorOptions options);
+ constructor(optional DOMString message = "", WidgetErrorOptions options);
 
  readonly attribute unsigned long long hardwareErrorCode;
  };