MINOR: Dont throw, if a Decoder has no style assigned (#1956)

Signed-off-by: Frauke Fritz <frauke.fritz@here.com>

@here/harp-datasource-protocol/lib/ITileDecoder.ts

@@ -62,7 +62,7 @@ export interface ITileDecoder {
         tileKey: TileKey,
         projection: Projection,
         requestController?: RequestController
-    ): Promise<DecodedTile>;
+    ): Promise<DecodedTile | undefined>;
 
     /**
      * Get tile info.

@here/harp-mapview-decoder/lib/ThemedTileDecoder.ts

@@ -12,6 +12,9 @@ import {
 } from "@here/harp-datasource-protocol";
 import { StyleSetEvaluator, StyleSetOptions } from "@here/harp-datasource-protocol/index-decoder";
 import { Projection, TileKey } from "@here/harp-geoutils";
+import { LoggerManager } from "@here/harp-utils";
+
+const logger = LoggerManager.instance.create("ThemedTileDecoder");
 
 /**
  * `ThemedTileDecoder` implements an [[ITileDecoder]] which uses a [[Theme]] to apply styles to the
@@ -35,9 +38,10 @@ export abstract class ThemedTileDecoder implements ITileDecoder {
         data: ArrayBufferLike,
         tileKey: TileKey,
         projection: Projection
-    ): Promise<DecodedTile> {
+    ): Promise<DecodedTile | undefined> {
         if (this.m_styleSetEvaluator === undefined) {
-            return Promise.reject(new Error("No style is defined"));
+            logger.info("cannot decode tile, as there is not style available");
+            return Promise.resolve(undefined);
         }
 
         return this.decodeThemedTile(data, tileKey, this.m_styleSetEvaluator, projection);

@here/harp-mapview-decoder/lib/TileDecoderService.ts

@@ -104,7 +104,7 @@ export class TileDecoderService extends WorkerService {
             }
         };
 
-        decodedTile.geometries.forEach(geom => {
+        decodedTile?.geometries.forEach(geom => {
             geom.vertexAttributes?.forEach(attr => transferBufferAttribute(attr));
             geom.interleavedVertexAttributes?.forEach(attr => transferBufferAttribute(attr));
             transferBufferAttribute(geom.index);
@@ -128,7 +128,7 @@ export class TileDecoderService extends WorkerService {
             }
         });
 
-        decodedTile.techniques.forEach(technique => {
+        decodedTile?.techniques.forEach(technique => {
             addBuffersToTransferList(technique, transferList);
         });
 

@here/harp-mapview-decoder/lib/TileLoader.ts

@@ -196,7 +196,10 @@ export class TileLoader extends BaseTileLoader {
      *
      * @param decodedTile - The [[DecodedTile]].
      */
-    private onDecoded(decodedTile: DecodedTile, onDone: (doneState: TileLoaderState) => void) {
+    private onDecoded(
+        decodedTile: DecodedTile | undefined,
+        onDone: (doneState: TileLoaderState) => void
+    ) {
         this.decodedTile = decodedTile;
         onDone(TileLoaderState.Ready);
     }

@here/harp-vectortile-datasource/test/VectorTileDecoderTest.ts

@@ -0,0 +1,21 @@
+/*
+ * Copyright (C) 2017-2020 HERE Europe B.V.
+ * Licensed under Apache 2.0, see full license in LICENSE
+ * SPDX-License-Identifier: Apache-2.0
+ */
+import { mercatorProjection, TileKey } from "@here/harp-geoutils";
+import { expect } from "chai";
+
+import { VectorTileDecoder } from "../index-worker";
+
+//    Mocha discourages using arrow functions, see https://mochajs.org/#arrow-functions
+
+describe("ThemedTileDecoder", function() {
+    it("#decodeTile does not throw", async function() {
+        const target = new VectorTileDecoder();
+
+        expect(
+            await target.decodeTile(new ArrayBuffer(0), new TileKey(0, 0, 0), mercatorProjection)
+        ).to.not.throw;
+    });
+});