### Question:
StringFormFieldController extends FormFieldController<String> { protected boolean isNullOrBlank() { final String fieldValue = getFieldValue(); return fieldValue == null || fieldValue.isBlank(); }  @Override void initialize(); abstract ObservableValue<String> getObservableValue(); @Override String getFieldValue();  }### Answer:
@Test public void isNullOrBlankMatches() { Stream.of(null, "", "\t \n ").forEach(nullOrBlank -> { sampleProp.setValue(nullOrBlank); assertThat(sampleFieldController.isNullOrBlank()).isTrue(); }); sampleProp.setValue("Non null nor empty/blank string"); assertThat(sampleFieldController.isNullOrBlank()).isFalse(); }