GrpcWebClientBase: add falsy response test

Author: pro-wh

javascript/net/grpc/web/grpcwebclientbase_test.js

@@ -75,6 +75,33 @@ testSuite({
     assertElementsEquals(DEFAULT_UNARY_HEADER_VALUES, Object.values(headers));
   },
 
+  async testRpcFalsyResponse() {
+    const xhr = new XhrIo();
+    const client = new GrpcWebClientBase(/* options= */ {}, xhr);
+    const methodDescriptor = createMethodDescriptor((bytes) => {
+      assertElementsEquals(DEFAULT_RPC_RESPONSE_DATA, [].slice.call(bytes));
+      return 0;
+    });
+
+    const response = await new Promise((resolve, reject) => {
+      client.rpcCall(
+          'url', new MockRequest(), /* metadata= */ {}, methodDescriptor,
+          (error, response) => {
+            assertNull(error);
+            resolve(response);
+          });
+      xhr.simulatePartialResponse(
+          googCrypt.encodeByteArray(new Uint8Array(DEFAULT_RPC_RESPONSE)),
+          DEFAULT_RESPONSE_HEADERS);
+      xhr.simulateReadyStateChange(ReadyState.COMPLETE);
+    });
+
+    assertEquals(0, response);
+    const headers = /** @type {!Object} */ (xhr.getLastRequestHeaders());
+    assertElementsEquals(DEFAULT_UNARY_HEADERS, Object.keys(headers));
+    assertElementsEquals(DEFAULT_UNARY_HEADER_VALUES, Object.values(headers));
+  },
+
   async testDeadline() {
     const xhr = new XhrIo();
     const client = new GrpcWebClientBase(/* options= */ {}, xhr);