Possibly a bug in generics resolution library?

ResolvingGenericParameterTypesTest.java

import java.lang.reflect.Method;
import java.lang.reflect.Type;
import java.util.HashMap;
import java.util.Map;

import org.junit.Test;
import ru.vyarus.java.generics.resolver.GenericsResolver;

import static org.junit.Assert.*;

public class ResolvingGenericParameterTypesTest {
    public static class Pair<F, S> {
        public final F first;
        public final S second;

        public Pair(F first, S second) {
            this.first = first;
            this.second = second;
        }
    }

    public static class PairProperties<F, S> {
        public void firstAndSecond(F first, S second) {
        }
    }

    public static class SelfPairProperties<F, S extends F> extends PairProperties<F, S> {
    }

    public static class IntegerPairProperties extends SelfPairProperties<Integer, Integer> {
    }

    @Test public void unresolvedPair() throws Exception {
        Map<String, Type> expected = new HashMap<>();
        expected.put("F", Object.class);
        expected.put("S", Object.class);

        Map<String, Type> actual =
            GenericsResolver.resolve(PairProperties.class)
                .method(firstAndSecond(PairProperties.class))
                .genericsMap();

        assertEquals(expected, actual);
    }

    @Test public void selfPair() throws Exception {
        Map<String, Type> expected = new HashMap<>();
        expected.put("F", Object.class);
        expected.put("S", Object.class);

        Map<String, Type> actual =
            GenericsResolver.resolve(SelfPairProperties.class)
                .method(firstAndSecond(SelfPairProperties.class))
                .genericsMap();

        assertEquals(expected, actual);
    }

    @Test public void integerPair() throws Exception {
        Map<String, Type> expected = new HashMap<>();
        expected.put("F", Integer.class);
        expected.put("S", Integer.class);

        Map<String, Type> actual =
            GenericsResolver.resolve(IntegerPairProperties.class)
                .method(firstAndSecond(IntegerPairProperties.class))
                .genericsMap();

        assertEquals(expected, actual);
    }

    private Method firstAndSecond(Class<?> target) throws Exception {
        return target.getMethod("firstAndSecond", Object.class, Object.class);
    }
}