title: Discord.js TypeError: Cannot read property 'setActivity' of null
body: <p>How can I fix this? I'm getting an error like <code>TypeError: Cannot read property 'setActivity' of null</code>.</p>
  
  <pre class="lang-js prettyprint-override"><code>client.on('ready', message  =&gt; {
    client.user.setActivity("21"+`${client.guilds.size} servers have members`+" "+"5"+`${client.users.size}`+` | !help `, { type: 'WATCHING' })
    console.log("21"+`${client.guilds.size} servers have members `+" "+"5"+`${client.users.size}`) 
  });
  </code></pre>