Mock Retrofit Service with Mockito

I tried with:

androidTestCompile 'org.mockito:mockito-core:2.0.26-beta'

public interface CustomerService {
  @POST("url")
  Observable<Session> createSession(@Body Credential credential);
}

@RunWith(AndroidJUnit4.class)
@LargeTest
public class LoginActivityTests {

@Before
public void setUp() {
    customerService = Mockito.mock(CustomerService.class);
}

@Test
public void testLoginGoToNextScreen() throws Exception {
   doReturn(new Session"token")).when(customerService).createSession(new Credential("aa", "123", new Device("asd", ":)")));
}

But it crash always.

java.lang.ExceptionInInitializerError
at org.mockito.internal.exceptions.stacktrace.ConditionalStackTraceFilter.<init>(ConditionalStackTraceFilter.java:17)
at org.mockito.exceptions.base.MockitoException.filterStackTrace(MockitoException.java:41)
at org.mockito.exceptions.base.MockitoException.<init>(MockitoException.java:30)
at org.mockito.internal.configuration.plugins.PluginLoader.loadPlugin(PluginLoader.java:35)
at org.mockito.internal.configuration.plugins.PluginRegistry.<init>(PluginRegistry.java:12)
at org.mockito.internal.configuration.plugins.Plugins.<clinit>(Plugins.java:11)
at org.mockito.internal.util.MockUtil.<clinit>(MockUtil.java:23)
at org.mockito.internal.MockitoCore.<init>(MockitoCore.java:44)
at org.mockito.Mockito.<clinit>(Mockito.java:1101)
at com.pickupnow.customer.LoginActivityTests.setUp(LoginActivityTests.java:48)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:24)
at android.support.test.internal.statement.UiThreadStatement.evaluate(UiThreadStatement.java:55)
at android.support.test.rule.ActivityTestRule$ActivityStatement.evaluate(ActivityTestRule.java:257)
at org.junit.rules.RunRules.evaluate(RunRules.java:20)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runners.Suite.runChild(Suite.java:128)
at org.junit.runners.Suite.runChild(Suite.java:27)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at org.junit.runner.JUnitCore.run(JUnitCore.java:115)
at android.support.test.internal.runner.TestExecutor.execute(TestExecutor.java:54)
at android.support.test.runner.AndroidJUnitRunner.onStart(AndroidJUnitRunner.java:228)
at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:1729)
Caused by: java.lang.NullPointerException
at org.mockito.internal.configuration.plugins.Plugins.getStackTraceCleanerProvider(Plugins.java:17)
at org.mockito.internal.exceptions.stacktrace.StackTraceFilter.<clinit>(StackTraceFilter.java:21)
... 41 more

Is there another way to do it?