Spring-Boot: Mockito Captor: NullPointerException and InvalidUseOfMatchersException

I'm trying to get familiar with Mockito Captor but I get both NullPointerException and InvalidUseOfMatchersException. I have a feeling, that I am doing something wrong and/or understanding the captor technique incorrectly.

Here is my testing class:

@Test
public void testFindByClientIdAndBatchDateBetween() {

    DateTime todayDateTime = new DateTime().withTimeAtStartOfDay();

    mockedTransactRepViewModel.capture().setClientId("123456");
    mockedTransactRepViewModel.capture().setBatchDate(todayDateTime.toDate());
    mockTransactRepViewRepository.save(mockedTransactRepViewModel.capture());

    verify(mockTransactRepViewRepository).findByClientIdAndClDateBetween("123456", todayDateTime.toDate(),
                                                                todayDateTime.plusDays(1).toDate()).get(0);

    String mockClientId = mockedTransactRepViewModel.getValue().getClientId();
    assertThat(mockClientId.equals("123456"));

    verify(mockTransactRepViewRepository, times(1)).save(mockedTransactRepViewModel.capture());
}