title: Python pandas split column with NaN values
body: <p>Hello my dear coders, </p>
  
  <p>I'm new to coding and I've stumbled upon a problem. I want to split a column of a csv file that I have imported via pandas in Python. The column name is <code>CATEGORY</code> and contains 1, 2 or 3 values such seperated by a comma (IE: 2343, 3432, 4959) Now I want to split these values into seperate columns named <code>CATEGORY</code>, <code>SUBCATEGORY</code> and <code>SUBSUBCATEGORY</code>.</p>
  
  <p>I have tried this line of code: </p>
  
  <pre><code>products_combined[['CATEGORY','SUBCATEGORY', 'SUBSUBCATEGORY']] = products_combined.pop('CATEGORY').str.split(expand=True)
  </code></pre>
  
  <p>But I get this error: <code>ValueError: Columns must be same length as key</code></p>
  
  <p>Would love to hear your feedback &lt;3</p>