public static String getRootLevelFieldName(String fieldName) {
    return fieldName.split("\\.")[0];
  }
@Test
  public void testGetRootLevelFieldName() {
    assertEquals("a", HoodieAvroUtils.getRootLevelFieldName("a.b.c"));
    assertEquals("a", HoodieAvroUtils.getRootLevelFieldName("a"));
    assertEquals("", HoodieAvroUtils.getRootLevelFieldName(""));
  }