why it has a NaN value when cut the data to bins : <p>I encounter a question:
<a href="https://i.stack.imgur.com/Wxblz.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Wxblz.png" alt="enter image description here"></a></p>

<p>why it has a NaN value</p>
