title: Getting this typeError: expected string or bytes-like object
body: <p>Code:</p>
  
  <pre><code>import pandas as pd
  import numpy as np
  import re
  
  df=pd.read_csv('twitDB.csv',header=None, sep=',',error_bad_lines=False,encoding='utf-8')
  
  hula=df[[0,1,2,3]]
  hula=hula.fillna(0)
  hula['tweet'] = hula[0].astype(str) +hula[1].astype(str)+hula[2].astype(str)+hula[3].astype(str) 
  dhole=hula["tweet"]
  
  
  dhole = re.sub('\s+', ' ',dhole )
  </code></pre>
  
  <p>Getting this:</p>
  
  <blockquote>
    <p>Error: expected string or bytes-like object</p>
  </blockquote>