public static Builder newTimestampColumnDefBuilder() {
    return new Builder();
  }
@Test
  public void build_column_def_with_only_required_attributes() {
    TimestampColumnDef def = newTimestampColumnDefBuilder()
      .setColumnName("created_at")
      .build();

    assertThat(def.getName()).isEqualTo("created_at");
    assertThat(def.isNullable()).isTrue();
    assertThat(def.getDefaultValue()).isNull();
  }