String projectId = "bigquery-public-data";
FileInputStream stream = new FileInputStream(<creds json path>);

BigQuery bigquery =
    BigQueryOptions.newBuilder()
        .setCredentials(ServiceAccountCredentials.fromStream(stream))
        .build()
        .getService();

Page<Dataset> page = bigquery.listDatasets(projectId);
for (Dataset dataset : page.iterateAll()) {
  assertThat(dataset.getLocation()).isNull();
}