add example on openapi 400 error

src/main/resources/openapi.yaml

@@ -2248,8 +2248,10 @@ components:
       properties:
         statusCode:
           type: integer
+          example: 400
         title:
           type: string
+          example: Bad Request
         invalidParams:
           type: array
           items:
@@ -2259,8 +2261,10 @@ components:
             properties:
               name:
                 type: string
+                example: '.title'
               reason:
                 type: string
+                example: 'Cannot be null'
 
   securitySchemes:
     JWTAuth: