@Udf(description = "Returns the current number of milliseconds for the system since "
      + "1970-01-01 00:00:00 UTC/GMT.")
  public long unixTimestamp() {
    return System.currentTimeMillis();
  }
@Test
  public void shouldReturnNull() {
    // When:
    final Long result = udf.unixTimestamp(null);

    // Then:
    assertNull(result);
  }