title: Handle Nan when using Pandas ExcelWriter in python
body: <p>How would I change the following code to handle NaN values as just empty cells within my dataframe as I iterate through it line by line outputting values in column A?</p>
  
  <pre><code>excel = pd.ExcelWriter(f_name,engine='xlsxwriter')
  wb = excel.book
  ws = wb.add_worksheet('PnL')
  
  for i in len(df):
    ws.write(0,i,df.iloc[i]['A'])
  </code></pre>