title: Python Pandas read_excel doesn't recognize null cell
body: <p>My excel sheet:</p>
  
  <pre><code>   A   B  
  1 first second
  2
  3 
  4  x   y  
  5  z   j
  </code></pre>
  
  <p>Python code:</p>
  
  <pre><code>df = pd.read_excel (filename, parse_cols=1)
  </code></pre>
  
  <p>return a correct output:</p>
  
  <pre><code>  first second
  0 NaN   NaN
  1 NaN   NaN
  2 x     y
  3 z     j
  </code></pre>
  
  <p>If i want work only with second column</p>
  
  <pre><code>df = pd.read_excel (filename, parse_cols=[1])
  </code></pre>
  
  <p>return:</p>
  
  <pre><code> second
  0  y
  1  j
  </code></pre>
  
  <p>I'd have information about empty excel rows (NaN in my df) even if I work only with a specific column.
  If output loose NaN information  it's not ok, for example, for skiprows paramater, etc</p>
  
  <p>Thanks</p>