title: How to treat NULL as a normal string with pandas?
body: <p>I have a csv-file with a column with strings and I want to read it with pandas. In this file the string <code>null</code> occurs as an actual value and should not be regarded as a missing value.</p>
  
  <p>Example:</p>
  
  <pre><code>import pandas as pd
  from io import StringIO
  
  data = u'strings,numbers\nfoo,1\nbar,2\nnull,3'
  print(pd.read_csv(StringIO(data)))
  </code></pre>
  
  <p>This gives the following output:</p>
  
  <pre><code>  strings  numbers
  0     foo        1
  1     bar        2
  2     NaN        3
  </code></pre>
  
  <p>What can I do to get the value <code>null</code> as it is (and not as NaN) into the DataFrame? The file can be assumed to not contain any actually missing values.</p>