Jukito Provider mock returns null

I am having some issues with a jukito unit test. I can't seem to mock Provider. Examples:.

import com.google.inject.Inject;
import com.google.inject.Provider;
import com.google.inject.Singleton;

@Singleton
public class ServiceClass1 {
    @Inject
    Provider<ConnectionClass> provider;

    public void method1() {
        Object o = provider.get().getO(); //during mainTest, provider is null and I get Nullpointer
    }
}

@Singleton
public class ConnectionClass {
    public Object getO() {
        //this is not relevant
    }
}

public class ConfigurationModule extends AbstractModule {
    bind(ServiceClass1.class).in(Singleton.class);
    bind(ConnectionClass.class).in(Singleton.class);
}

@RunWith(JukitoRunner.class)
public class ServiceClass1Test {
    @InjectMocks
    ServiceClass1 service;

    @Mock
    Provider<ConnectionClass> connectionClassProvider;

    @Mock
    ConnectionClass connectionClass;

    @Before
    public void setup() {
        MockitoAnnotations.initMocks(this);
        when(connectionClassProvider.get()).thenReturn(connectionClass); 
    }

    @Test
    public void mainTest() {
        service.method1();
    }
}

I expect to get a mocked connection class, but instead provider returns null. I tried binding connectionClass to TestSingleton, but that does not help. Inside test class:

public static class Module extends JukitoModule {
    @Override
    protected void configureTest() {
        bindMock(ConnectionClass.class).in(TestSingleton.class);
    }
}

If anyone has some suggestions for me, I would greatly appreciate it.

Using constructor injection instead of field injection:

@Singleton
public class ServiceClass1 {

    Provider<ConnectionClass> provider;

    @Inject
    public ServiceClass1(Provider<ConnectionClass> provider) {
        this.provider = provider;
    }
}

and dropping InjectMocks:

@Mock
Provider<ConnectionClass> provider;

ServiceClass1 serviceClass1;

@Before
public void setup() {
    MockitoAnnotations.initMocks(this);
    serviceClass1 = new ServiceClass1(provider);
}

makes everything work. Can InjectMocks be the cause of this? Anyway, I guess this will do for now.