@java.lang.Override
    public com.google.protobuf.ByteString getPubsubTopicBytes() {
      java.lang.Object ref = pubsubTopic_;
      if (ref instanceof java.lang.String) {
        com.google.protobuf.ByteString b =
            com.google.protobuf.ByteString.copyFromUtf8((java.lang.String) ref);
        pubsubTopic_ = b;
        return b;
      } else {
        return (com.google.protobuf.ByteString) ref;
      }
    }
<pre>
Required. The `Topic.name` of the Pub/Sub topic to which to publish
notifications. Must be of the format: `projects/{project}/topics/{topic}`.
Not matching this format results in an
[INVALID_ARGUMENT][google.rpc.Code.INVALID_ARGUMENT] error.
</pre>

<code>string pubsub_topic = 1 [(.google.api.field_behavior) = REQUIRED];</code>

@return The bytes for pubsubTopic.
java-storage-transfer/proto-google-cloud-storage-transfer-v1/src/main/java/com/google/storagetransfer/v1/proto/TransferTypes.java