title: numpy.where: TypeError: invalid type promotion
body: <p><sub> I know there are other questions with the same error name, yet none of them match the np.where statement, and also I couldn't find the answer to my problem in them</sub><p>
  So I made a pandas <code>DataFrame</code> called <code>data</code> and created a <code>Series</code> out of it called <code>dates</code>, which is:</p>
  
  <pre><code>dates= pd.to_datetime(pd.to_timedelta(data.a_date, unit= 'D') + pd.datetime(1960,1,1), 
                        errors= 'coerse')
  </code></pre>
  
  <p>I need to clear some of the dates because they do not match with an indicator of them in <code>data</code>, so I tried to adjust that while keeping the indexes correct using <code>numpy.where</code>,<br>
  Yet I had gotten this error:</p>
  
  <pre><code>---------------------------------------------------------------------------
  TypeError                                 Traceback (most recent call last)
  &lt;ipython-input-18-2b83ed2b2468&gt; in &lt;module&gt;()
  ----&gt; 1 np.where(((dates.notnull()) &amp; (data.a_IND == 0)), np.nan, dates)
  
  TypeError: invalid type promotion
  </code></pre>