fix(mybatis): 修复匿名用户处理逻辑返回null值问题

- 修改AnonymousAuthenticationToken情况下的返回值为null
- 优化authentication对象存在性检查逻辑

pigx-common/pigx-common-data/src/main/java/com/pig4cloud/pigx/common/data/mybatis/MybatisPlusMetaObjectHandler.java

@@ -81,7 +81,7 @@ public class MybatisPlusMetaObjectHandler implements MetaObjectHandler {
 		Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
 		// 匿名接口直接返回
 		if (authentication instanceof AnonymousAuthenticationToken) {
-			return authentication.getName();
+			return null;
 		}
 
 		if (Optional.ofNullable(authentication).isPresent()) {