I have the following class:

import java.util.HashMap;

public class Foo extends HashMap<Bar, Baz> {
}

Flink cannot serialize this class without further help or resorting to Kryo, this test fails:

import org.apache.flink.types.PojoTestUtils;
import org.junit.jupiter.api.Test;

class FooTest {
    @Test
    void test() {
            PojoTestUtils.assertSerializedAsPojoWithoutKryo(Foo.class);
    }
}

I tried the following to no avail:

import org.apache.flink.api.common.typeinfo.TypeInfo;
import org.apache.flink.api.common.typeinfo.TypeInfoFactory;
import org.apache.flink.api.common.typeinfo.TypeInformation;
import org.apache.flink.api.common.typeinfo.Types;

import java.lang.reflect.Type;
import java.util.HashMap;
import java.util.Map;
@TypeInfo(Foo.FooTypeInfoFactory.class)
public class Foo extends HashMap<Bar, Baz> {
        public static class FooTypeInfoFactory extends
                TypeInfoFactory<Foo> {
            @Override
            public TypeInformation<Foo> createTypeInfo(Type type, Map<String, TypeInformation<?>> map) {
                var type = (TypeInformation<Foo>)
                        Types.MAP(TypeInformation.of(Bar.class), TypeInformation.of(Baz.class));
                return type;
            }
        }
}

But this does not work because

Inconvertible types; cannot cast 'org.apache.flink.api.common.typeinfo.TypeInformation<java.util.Map<Bar,Baz>>' to 'org.apache.flink.api.common.typeinfo.TypeInformation<Foo>'

Is there some way to make this idea work? Foo implements Map<Bar, Baz> so it seems to me that I should be able to tell Flink somehow, that it should be serialized like a Map.