title: Count all NaNs in a pandas DataFrame
body: <p>I'm trying to count  NaN  element (data type class 'numpy.float64')in pandas series to know how many are there
  which data type is class 'pandas.core.series.Series'</p>
  
  <p>This is for count null value in pandas series</p>
  
  <pre class="lang-py prettyprint-override"><code>import pandas as pd
  oc=pd.read_csv(csv_file)
  oc.count("NaN")
  
  </code></pre>
  
  <p>my expected output of <code>oc,count("NaN")</code> to be 7 but it show <code>'Level NaN must be same as name (None)'</code></p>