Updating from 2.X to 3.X breaks due to change of Serializer

[SElab2019]

When I try to upgrade mapdb from 2.X to 3.X. The following code breaks.

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.io.Serializable;

import org.mapdb.Serializer;

public class TestMapdb extends Serializer<String> implements Serializable{

    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    public void serialize(DataOutput out) throws IOException {
        // TODO Auto-generated method stub

    }

    @Override
    public String deserialize(DataInput in, int available) throws IOException {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public void serialize(DataOutput out, String value) throws IOException {
        // TODO Auto-generated method stub

    }

}

The code should pass, but it throws an error:

TestMapdb.java:[10,42] no interface expected here