Mockito - How to spy on Invocation argument in doAnswer

This is my first day writing Unit tests using Mockito and I might have started with a complex exercise.

Below is my class structure and I am writing tests for Class2.targetMethod(). Class1 static method modifies passed in object instead of returning any results.

class Class1 {
    static void dbquery(OutParam out) {
        // Complex code to fill in db results in OutParam object
    }
}

class Class2 {
    void targetMethod() {
        OutParam p1 = new OutParam1();
        Class1.dbquery(p1);
        ResultSet rs = p1.getCursor();
        ...
    }
}

Below is my setup for the tests:

@RunWith(PowerMockRunner.class)
@PrepareForTest({Class1.class, Class2.class})
public class Class2Test {
    @Before
    public void setUp() throws Exception {

        PowerMockito.mockStatic(Class1.class);

        doAnswer(new Answer<Void>() {
            @Override
            public Void answer(InvocationOnMock invocation) throws Exception {
                OutParam result = (OutParam)invocation.getArguments()[1];
                OutParam spy = spy(result);
                ResultSet mockResult = mock(ResultSet.class);
                doReturn(mockResult).when(spy.getCursor());
                when(mockResult.getString("some_id")).thenReturn("first_id","second_id");
                when(mockResult.getString("name")).thenReturn("name1","name2");

                return null;
            }
        }).when(Class1.class, "dbquery", any());
    }
}

However the tests fail with exception below - mainly due to "doReturn" line.

Any suggestions on this problem or if my approach is completely wrong.

org.mockito.exceptions.misusing.UnfinishedStubbingException: 
Unfinished stubbing detected here:

E.g. thenReturn() may be missing.
Examples of correct stubbing:
    when(mock.isOk()).thenReturn(true);
    when(mock.isOk()).thenThrow(exception);
    doThrow(exception).when(mock).someVoidMethod();
Hints:
 1. missing thenReturn()
 2. you are trying to stub a final method, you naughty developer!
 3: you are stubbing the behaviour of another mock inside before 'thenReturn' instruction if completed