@Test
public void isNotDefinedIfContextHasNoThing() {

    final CommandStrategy.Context<ThingId> context = getDefaultContext();
    final RetrieveThing command = RetrieveThing.of(context.getState(), DittoHeaders.empty());
    final boolean defined = underTest.isDefined(context, null, command);
    assertThat(defined).isFalse();
}