title: float object has no attribute isna
body: <p>I have a df where all columns are objects. Why can't I apply a function that checks whether 2 column have a NaN. I want to avoid <code>np.where</code> since I have has 6 other elif lines in the function.</p>
  <pre><code>df
      cola_              check1             colb           check2          
  0   The start          hungry             banana          high         
  1    world             NaN                apple           NaN         
  2   yesterday          fruit              pear            high        
  </code></pre>
  <pre><code>def func(df):
       if (df['check1'].isna()) &amp; (df['check2'].isna()):
            return df['colb']
  </code></pre>
  <pre><code>df['final'] = df.apply(func, axis=1)
  </code></pre>
  <p>Expected Output</p>
  <pre><code>    cola_             check1              colb           check2     final
  0   The start          hungry             banana         high        
  1    world             NaN                apple           NaN        apple    
  2   yesterday          fruit              pear            high       
  
  
  'float' object has no attribute 'isna'
  </code></pre>