为什么Jackson仍然将long[]序列化为数字数组?

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.module.SimpleModule;
import com.fasterxml.jackson.databind.ser.std.ToStringSerializer;

import java.io.IOException;

public class Application {
    public static void main(String[] args) throws IOException {
        SimpleModule module = new SimpleModule();

        module.addSerializer(Long.class, ToStringSerializer.instance);
        module.addSerializer(Long.TYPE, ToStringSerializer.instance);

        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.registerModule(module);

        Long l1 = 1L;
        long l2 = 1L;
        Long[] ls1 = new Long[]{1L, 2L};
        long[] ls2 = new long[]{1L, 2L};

        System.out.println(objectMapper.writeValueAsString(l1));
        System.out.println(objectMapper.writeValueAsString(l2));
        System.out.println(objectMapper.writeValueAsString(ls1));
        System.out.println(objectMapper.writeValueAsString(ls2));
    }
}

对于此代码片段,输出为:

"1"
"1"
["1","2"]
[1,2]

你能解释一下为什么ls2被序列化为[1,2]吗?我认为应该是[“1”,2]。