public static Read<String> readStrings() {
    return Read.newBuilder(
            (PubsubMessage message) -> new String(message.getPayload(), StandardCharsets.UTF_8))
        .setCoder(StringUtf8Coder.of())
        .build();
  }
@Test
  public void testNullTopic() {
    String subscription = "projects/project/subscriptions/subscription";
    PubsubIO.Read<String> read =
        PubsubIO.readStrings().fromSubscription(StaticValueProvider.of(subscription));
    assertNull(read.getTopicProvider());
    assertNotNull(read.getSubscriptionProvider());
    assertNotNull(DisplayData.from(read));
  }