[BUG]对象字段大小写转换不一致

### 问题描述
字段首字母小写第二个字母大写，转换后第二个字母变成小写

### 环境信息
*请填写以下信息：*

- JDK信息： 1.8
- 版本信息：2.0.14

### 重现步骤
定义对象

1. springboot配置
```java
@Configuration
public class JsonCounfig implements WebMvcConfigurer {

@Override
public void configureMessageConverters(List> converters) {
//删除jackson的消息转换器
converters.removeIf(item -> item instanceof MappingJackson2HttpMessageConverter);
//定义一个converters转换消息的对象
FastJsonHttpMessageConverter fastJsonHttpMessageConverter = new FastJsonHttpMessageConverter();
//添加fastjson的配置信息，比如: 是否需要格式化返回的json数据
FastJsonConfig fastJsonConfig = new FastJsonConfig();
fastJsonConfig.setDateFormat(DatePattern.NORM_DATETIME_PATTERN);

//在converter中添加配置信息
fastJsonHttpMessageConverter.setFastJsonConfig(fastJsonConfig);
List mediaTypes = new ArrayList<>();
mediaTypes.add(MediaType.valueOf(MediaType.APPLICATION_JSON_VALUE + ";charset=UTF-8"));
fastJsonHttpMessageConverter.setSupportedMediaTypes(mediaTypes);
//fastjson转换器必须放在StringHttpMessageConverter之后，不然接口返回值如果是字符串，会多加一对双引号
converters.add(fastJsonHttpMessageConverter);
}
}

```
2.定义对象Demo
```java
public class Demo{
private String eAccId;
}
```
3.Controller请求返回
```json
"result": {
"EAccId": "张三"
}
```

### 期待的正确结果
```json
"result": {
"eAccId": "张三"
}
```

Reproduce the issue with the shown Spring Boot converter configuration and the Demo class containing the eAccId field. Trace the Java field-name serialization path, then verify that the response property remains eAccId rather than becoming EAccId.

Written by the indexing model from the issue text.