import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.when;
-import com.google.common.base.Optional;
import java.math.BigInteger;
import java.util.Collections;
import java.util.List;
+import java.util.Optional;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;