fix: 修复 example /json Required request body is missing

app/src/main/java/com/yiring/app/web/example/ExampleController.java

@@ -84,7 +84,9 @@ public class ExampleController {
 
     @ApiOperation(value = "JSON 传参")
     @PostMapping("json")
-    public Result<PageVo<String>> json(@RequestBody @Validated(Group.Optional.class) PageParam param) {
+    public Result<PageVo<String>> json(
+        @RequestBody(required = false) @Validated(Group.Optional.class) PageParam param
+    ) {
         return page(param);
     }