title: Why git pull fails?
body: <p>Today, supposingly I faced with a git problem. It's 1 year I use git <em>(just <code>push</code> and <code>pull</code> commands)</em> and all been fine so far. But today this command doesn't work and throws an error:</p>
  
  <pre><code>$ git pull origin master
  </code></pre>
  
  <p>Here is the error:</p>
  
  <p><a href="https://i.stack.imgur.com/zlF5G.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/zlF5G.png" alt="enter image description here"></a></p>
  
  <p>Does anybody know what's the problem and how can I fix it?</p>