title: How to count the null,na and nan values in each column of pyspark dataframe
body: <p>Dataframe as na,Nan and Null values .
  Schema (Name:String,Rol.No:Integer,Dept:String
  Example:</p>
  
  <pre><code>Name  Rol.No  Dept
  priya  345     cse
  James  NA       Nan
  Null   567      NULL
  </code></pre>
  
  <p>Expected output as to columns name and count of null,na and nan values</p>
  
  <pre><code>Name 1
  Rol.No 1
  Dept 2
  </code></pre>