message: Handle undefined imageSource
diff: @@ -140,14 +140,17 @@ class WebMercatorTileLoader extends TileLoader {
  const quadId = new QuadId(missingTile.id);
  const corners = quadId.getEcefCorners();
  const imageSource = await this.imageryProvider.loadTile(quadId.row, quadId.column, quadId.level);
  + if (undefined === imageSource) {
  + missingTile.setNotFound();
  + } else {
  const textureLoad = this.loadTextureImage(imageSource as ImageSource, this.model, IModelApp.renderSystem);
  this.ecefToDb.multiplyPoint3dArrayInPlace(corners as Point3d[]);
  textureLoad.catch((_err) => missingTile.setNotFound());
  textureLoad.then((result) => {
  - // Make sure we still want this tile - may been unloaded, imodel may have been closed, IModelApp may have shut down taking render system with it, etc.
  missingTile.setGraphic(IModelApp.renderSystem.createTile(result as RenderTexture, corners as Point3d[]));
  });
  }
  + }
  }));
  }
  