Create a dummy for listeners or callbacks

Dummy.java

import com.google.common.base.Defaults;
import com.google.common.primitives.Primitives;

import java.lang.reflect.Array;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public final class Dummy {

    private Dummy() {}

    @SuppressWarnings("unchecked")
    public static <T> T of(Class<T> type) {
        return (T) Proxy.newProxyInstance(
            type.getClassLoader(),
            new Class<?>[]{type},
            new InvocationHandler() {
                @Override
                public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                    final Class<?> returnType = Primitives.unwrap(method.getReturnType());

                    if (returnType.isPrimitive()) {
                        return Defaults.defaultValue(returnType);
                    } else if (returnType.isArray()) {
                        return Array.newInstance(returnType.getComponentType(), 0);
                    } else {
                        return null;
                    }
                }
            });
    }
}