Strapi GraphQL find single item by slug

schema.graphql.js

const { sanitizeEntity } = require('strapi-utils');

module.exports = {
  query:  `
    categoryBySlug(slug: String!): Category
  `,
  resolver: {
    Query: {
      categoryBySlug: {
        resolverOf: 'Category.findOne',
        async resolver(_, { slug }) {
          const entity = await strapi.services.category.findOne({ slug });
          return sanitizeEntity(entity, { model: strapi.models.category });
        },
      },
    }
  },
};