Fastify openapi 3 create alway required fields

Question

i use @fastify/swagger and @fastify/swagger-ui, my config

import fastifySwagger from '@fastify/swagger';
import fastifySwaggerUi from '@fastify/swagger-ui';
import { FastifyInstance } from 'fastify';
import fp from 'fastify-plugin';

const swagger = async (fastify: FastifyInstance) => {
  await fastify.register(fastifySwagger, {
    mode: 'dynamic',
    openapi: {
      openapi: '3.0.3',
      info: {
        title: 'openapi',
        version: '0.1.0'
      }
    }
  });

  await fastify.register(fastifySwaggerUi, {
    routePrefix: '/openapi',
    uiConfig: {
      deepLinking: true
    },
    uiHooks: {
      onRequest: function (request, reply, next) {
        next();
      },
      preHandler: function (request, reply, next) {
        next();
      }
    },
    staticCSP: true,
    transformStaticCSP: (header) => header,
    transformSpecification: (swaggerObject, request, reply) => {
      return swaggerObject;
    },
    transformSpecificationClone: true
  });
};

export default fp(swagger);

my routes like this

export const articleRouter = async (fastify: FastifyInstance) => {
  fastify.get(
    '/list',
    {
      schema: {
        tags: ['article'],
        summary: 'getting artilce list',
        description: 'description in routes',
        params: {
          type: 'object',
          description: 'some params',
          properties: {
            limit: {
              type: 'number',
              description: 'limit articles'
            },
            sort: {
              type: 'string',
              description: 'asc or desc'
            }
          },
          required: ['sort']
        },
      }
    },
    async (req, resp) => {
      const articles = await articleService.findArticles();
      resp.send(articles);
    }
  );
};

swagger screenshot

enter image description here

All works, but field 'limit' is alway required. Why?

Please, help me.

I'm playing with all properties in config and routes but no one helpe me.

@fastify/swagger @fastify/swagger-ui