Stop dereferencing an optional parameter without checking it

src/node/src/client.js

@@ -280,7 +280,9 @@ function makeUnaryRequestFunction(method, serialize, deserialize) {
       }
       var client_batch = {};
       var message = serialize(argument);
-      message.grpcWriteFlags = options.flags;
+      if (options) {
+        message.grpcWriteFlags = options.flags;
+      }
       client_batch[grpc.opType.SEND_INITIAL_METADATA] = metadata;
       client_batch[grpc.opType.SEND_MESSAGE] = message;
       client_batch[grpc.opType.SEND_CLOSE_FROM_CLIENT] = true;
@@ -416,7 +418,9 @@ function makeServerStreamRequestFunction(method, serialize, deserialize) {
       }
       var start_batch = {};
       var message = serialize(argument);
-      message.grpcWriteFlags = options.flags;
+      if (options) {
+        message.grpcWriteFlags = options.flags;
+      }
       start_batch[grpc.opType.SEND_INITIAL_METADATA] = metadata;
       start_batch[grpc.opType.RECV_INITIAL_METADATA] = true;
       start_batch[grpc.opType.SEND_MESSAGE] = message;