code: public java.util.List<String> getTopicNames() {
          if (topicNames == null) {
              topicNames = new com.amazonaws.internal.SdkInternalList<String>();
          }
          return topicNames;
      }
docs: <p>
  A list of SNS topic names for which to obtain the information. If this member is null, all associations for the
  specified Directory ID are returned.
  </p>
  <p>
  An empty list results in an <code>InvalidParameterException</code> being thrown.
  </p>
  
  @return A list of SNS topic names for which to obtain the information. If this member is null, all associations
  for the specified Directory ID are returned.</p>
  <p>
  An empty list results in an <code>InvalidParameterException</code> being thrown.