SpringMvc中全局设置了`JSONWriter.Feature.WriteMapNullValue`，如何单独指定某个类型设置不过滤NULL（也就是fastjson）默认序列化方式

### SpringMvc中全局设置了`JSONWriter.Feature.WriteMapNullValue`，不过滤`NULL`值，
如何针对某个类型过滤NULL值，`JSONWriter.Feature`中是否存在过滤NULL的值
```java
@Bean
public FastJsonHttpMessageConverter fastJsonHttpMessageConverter(){
FastJsonHttpMessageConverter converter = new FastJsonHttpMessageConverter();
//自定义配置
FastJsonConfig config = new FastJsonConfig();
config.setDateFormat("yyyy-MM-dd HH:mm:ss");
config.setReaderFeatures(JSONReader.Feature.FieldBased, JSONReader.Feature.SupportArrayToBean);
config.setWriterFeatures(JSONWriter.Feature.WriteMapNullValue);
converter.setFastJsonConfig(config);
converter.setDefaultCharset(StandardCharsets.UTF_8);
converter.setSupportedMediaTypes(Collections.singletonList(MediaType.APPLICATION_JSON));
return converter;
}
`

Start with the FastJsonHttpMessageConverter and FastJsonConfig setup shown in the issue, then inspect the JSONWriter.Feature options related to null handling. Determine how a single type can override the global WriteMapNullValue setting, and confirm that the resulting serialization matches the default null-filtering behavior.

Written by the indexing model from the issue text.