real method invoke mock method but not work - mockito

Question

i spy a object to test a method
List<HighWay> mockedList = mock(List.class);
request = Mockito.spy(new HighWayRequest());
Mockito.doReturn(mockedList).when(request).getHighWays();
request.updateNewHighWay(repository);
the updateNewHighWay method invoke getHighWays method which i want to return list,
and real method of request is like that
public void updateNewHighWay(HighWayRepository repository) {
List<HighWay> total = getHighWays();
List<HighWay> willSave = new ArrayList<HighWay>();
for (HighWay highWay : total) {
if (!repository.exists(highWay.getId())) {
willSave.add(highWay);
repository.save(highWay);
}
}
while (total.size() == willSave.size()) {
total = getHighWays();
willSave = new ArrayList<HighWay>();
for (HighWay highWay : total) {
if (!repository.exists(highWay.getId())) {
willSave.add(highWay);
repository.save(highWay);
}
}
}
}
public List<HighWay> getHighWays() {
// TODO Auto-generated method stub
return null;
}
but the reality it throws nullexception.
java.lang.NullPointerException at
chinahighway.HighWayRequest.updateNewHighWay(HighWayRequest.java:206)
at chinahighway.HttpTest.testpageinsert(HttpTest.java:269) at
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606) at
org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
at
org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at
org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
at
org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at
org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:73)
at
org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:82)
at
org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:73)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271) at
org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:217)
at
org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:83)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238) at
org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63) at
org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236) at
org.junit.runners.ParentRunner.access$000(ParentRunner.java:53) at
org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229) at
org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
at
org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:68)
at org.junit.runners.ParentRunner.run(ParentRunner.java:309) at
org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:163)
at
org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
at
org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
at
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675)
at
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
at
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
why the doReturn not work? how to let getHighWays method return my wanted list?
plz help me thanks very much!