message: undefined test for crash in Swego files.
diff: @@ -181,7 +181,7 @@ export namespace IModelTileIO {
  }
  protected materialFromJson(key: string): RenderMaterial | undefined {
  - if (this.renderMaterials[key] === undefined)
  + if (this.renderMaterials === undefined || this.renderMaterials[key] === undefined)
  return undefined;
  let material = this.system.findMaterial(key, this.model.iModel);
  