static MetricsConfig create(String prefix) {
    return loadFirst(prefix, "hadoop-metrics2-" +
        StringUtils.toLowerCase(prefix) + ".properties", DEFAULT_FILE_NAME);
  }
@Test public void testMissingFiles() {
    MetricsConfig config = MetricsConfig.create("JobTracker", "non-existent.properties");
    assertTrue(config.isEmpty());
  }