title: I get an arror for map function(posts.map is not a function)
body: <p>I get this error, while I don't see any issue in that:</p>
  <p><code>posts.map is not a function</code></p>
  <pre><code>import React from 'react'
  import { useSelector } from 'react-redux'
  
  export const PostsList = () =&gt; {
    const posts = useSelector(state =&gt; state.posts)
  
    const renderedPosts = posts.map(post =&gt; (
      &lt;article className=&quot;post-excerpt&quot; key={post.id}&gt;
        &lt;h3&gt;{post.title}&lt;/h3&gt;
        &lt;p className=&quot;post-content&quot;&gt;{post.content.substring(0, 100)}&lt;/p&gt;
      &lt;/article&gt;
    ))
  
    return (
      &lt;section className=&quot;posts-list&quot;&gt;
        &lt;h2&gt;Posts&lt;/h2&gt;
        {renderedPosts}
      &lt;/section&gt;
    )
  }
  </code></pre>
  <p>This is my code Sandbox: <a href="https://codesandbox.io/s/wandering-darkness-6hi04d?file=/src/features/posts/PostsList.js" rel="nofollow noreferrer">https://codesandbox.io/s/wandering-darkness-6hi04d?file=/src/features/posts/PostsList.js</a></p>