public static String emptyToNull(String string) {
    return string == null || string.isEmpty() ? null : string;
  }
@Test
  void emptyToNullInputNullOutputNull() {
    // Arrange
    final String string = null;
    // Act
    final String retval = Util.emptyToNull(string);
    // Assert result
    assertThat(retval).isNull();
  }