@Test
public void toStringTestWithNulls() {

    UntypedValues values = UntypedValues.builder()
            .values(Collections.singletonMap("key", null))
            .build();
    String string = values.toString();
    assertNotNull(string);
    System.out.println(string);
    assertEquals(
            "UntypedValues(source=null, timestamp=0, prefix=null, values={key=null})",
            string
    );
}