title: Pandas keep 'null' and ' ' when loading CSV
body: <p>I have a weird CSV that has "null" as a value, as well it has an empty cell as a value. </p>
  
  <p>So my row looks like this:</p>
  
  <pre><code>null,0,0,0,1,,,,0,0,0,null
  </code></pre>
  
  <p>I'm doing nothing but reading and rewriting a file:</p>
  
  <pre><code>f = pd.read_csv(input_file,sep=',', quotechar='"', engine='python', converters={i: str for i in range(0, 155)})
  f.to_csv(output_file, sep=',', escapechar=' ', quotechar='"', quoting=csv.QUOTE_MINIMAL, index=False)
  </code></pre>
  
  <p>Above is technically "renaming" a file, but this is to prove that I'm getting the same values for the whole file, later I'll trim certain columns (which I did already, but figured out data is wrong). </p>
  
  <p>So, how do I preserve both "null", and " " without reading each row/column, and making a function that checks every single cell?</p>
  
  <p>Is that even possible?</p>
  
  <p>I tried na_rep="null", but then all '' are converted to 'null', or if I drop them, then I loose my 'null' values. </p>