title: ufunc 'isnan' not supported for the input types when checking for NaN-inputs in a dataset
body: <p>I'm trying to do something as simple as checking the titanic dataset for NaN values in python (I know they are in the &quot;age&quot; column, so this is more to practice).</p>
  <p>When using np.isnan im getting:
  <em>TypError: ufunc 'isnan' not supported for the input types, and the inputs could not be safely coerced to any supported types according to the casting rule ''safe''</em></p>
  <pre><code>ds = sn.load_dataset(&quot;titanic&quot;)
  for i in range(0,len(ds.index)):
      for j in range(0, len(ds.columns)):
          # Check if cell is NaN
          if np.isnan(ds.iloc[i][j]):
              print(&quot;it works, yay&quot;)
  </code></pre>
  <p>Why doesn't this work?</p>