message: fix, proper EmptyRepresentationProvider
diff: @@ -65,12 +65,16 @@ export namespace RepresentationProvider {
  export type AnyRepresentationProvider = RepresentationProvider<any, {}, Representation.State>
  -const EmptyRepresentationProvider = {
  +export const EmptyRepresentationProvider: RepresentationProvider = {
  + name: '',
  label: '',
  description: '',
  factory: () => Representation.Empty,
  getParams: () => ({}),
  - defaultValues: {}
  + defaultValues: {},
  + defaultColorTheme: ColorTheme.EmptyProvider,
  + defaultSizeTheme: SizeTheme.EmptyProvider,
  + isApplicable: () => true
  };
  function getTypes(list: { name: string, provider: RepresentationProvider<any, any, any> }[]) {
  @@ -114,7 +118,7 @@ export class RepresentationRegistry<D, S extends Representation.State> {
  }
  get<P extends PD.Params>(name: string): RepresentationProvider<D, P, S> {
  - return this._map.get(name) || EmptyRepresentationProvider as unknown as RepresentationProvider<D, P, S>;
  + return this._map.get(name) || EmptyRepresentationProvider;
  }
  get list() {
  