title: Expected behavior of Pandas str.isnumeric()
body: <p>I have a multi-dtype series <code>pd.Series</code> like <code>[100, 50, 0, foo, bar, baz]</code></p>
  
  <p>when I run <code>pd.Series.str.isnumeric()</code></p>
  
  <p>I get <code>[NaN, NaN, NaN, False, False, False]</code></p>
  
  <p>Why is this happening? Shouldn't it return <code>True</code> for the first three in this series?</p>