json – Cannot read property ‘title’ of null using vuejs 3

i am new to vuejs3, i tried using json with vuejs3, i displayed the courses in view blog / index, and when clicking on a course in an index it redirect to details of that course clicks, in my case it gives me error: Uncaught (in promise) TypeError: Cannot read property 'title' of null.

blog/index.vue

<template lang="">
    <div class="row">
       <div class="col-md-6" v-for="post in posts">
          <h1><router-link :to="{ name: 'post-show', params: { id: post.id, slug: post.slug }}">{{ post.title }}</router-link></h1>
          <p class="lead">{{ post.content }}</p>
       </div>
    </div>
</template>
<script>
export default {
    data() {
      return {
         posts: ()
      }
    },
    mounted() {
       fetch('http://localhost:5000/posts')
          .then(res => res.json())
          .then(data => this.posts = data)
          .catch(err => console.log(err))
    },
}
</script>

blog/show.vue

<template lang="">
   <h1>{{ post.title }}</h1>
   <p>{{ post.content }}</p>
</template>
<script>
export default {

    props: ('id', 'slug'),
    data(){
        return {
            post: null
        }
    },
    mounted() {
        fetch(`http://localhost:5000/posts/${this.id}`)
          .then(res => res.json())
          .then(data => this.post = data)
          .catch(err => console.log(err))
    }
}
</script>

Router/index.js

  {
        path: '/blog/:id/:slug',
        name: 'post-show',
        component: Show,
        props: true
      },
**data/db.json**
{
    "posts": (
        {
           "id": 1,
           "title"  : "learn angular",
           "slug"   : "learn-angular",
           "content": "Lorem ipsum dolor sit amet consectetur adipisicing elit. Ratione, possimus."
        },
        {
           "id": 2,
           "title"  : "learn react",
           "slug"   : "learn-react",
           "content": "Lorem ipsum dolor sit amet consectetur adipisicing elit. Ratione, possimus."
        },
        {
           "id": 3,
           "title"  : "learn laravel",
           "slug"   : "learn-laravel",
           "content": "Lorem ipsum dolor sit amet consectetur adipisicing elit. Ratione, possimus."
        },
        {
           "id": 4,
           "title"  : "learn symfony",
           "slug"   : "learn-symfony",
           "content": "Lorem ipsum dolor sit amet consectetur adipisicing elit. Ratione, possimus."
        },
        {
           "id": 5,
           "title"  : "learn jee",
           "slug"   : "learn-jee",
           "content": "Lorem ipsum dolor sit amet consectetur adipisicing elit. Ratione, possimus."
        },
        {
           "id": 6,
           "title"  : "learn php",
           "slug"   : "learn-oracle",
           "content": "Lorem ipsum dolor sit amet consectetur adipisicing elit. Ratione, possimus."
        }
     ),
     "users": ()
}