title: 'NoneType' object has no attribute 'fillna' Error
body: <p>I am getting an error in the following code. Not able to understand why. Getting an error at the last line of the code. Please advise what has to be done to correct it. In addition to this df.isna().any() is also not working.</p>
  
  <pre><code>import pandas as pd
  import numpy as np
  import matplotlib.pyplot as plt
  
  %matplotlib inline
  
  data = pd.read_csv('BlackFriday.csv')
  df = pd.DataFrame(data)
  
  df.info()
  df.describe()
  df.head()
  
  #To check the unique values of Product Categories 2, 3 and then assign a default value accordingly for NaN's
  
  Product_Category_2 = df['Product_Category_2'].unique()
  Product_Category_3 = df['Product_Category_3'].unique()
  print('Product_Category_2', Product_Category_2)
  print('Product_Category_3', Product_Category_3)
  
  df = df.fillna(0, inplace=True)
  
  
  
  
  ---------------------------------------------------------------------------
  AttributeError                            Traceback (most recent call last)
  &lt;ipython-input-16-7f28e582ea84&gt; in &lt;module&gt;()
        1 #We can replace the NaN's with 0.
  ----&gt; 2 df = df.fillna(0, inplace=True)
        3 
  
  AttributeError: 'NoneType' object has no attribute 'fillna'
  
  
  </code></pre>