title: Checking for both NaT or pandas timestamp
body: <p>How can I validate for NaT in python while at the same time working for timestamps. E.g. the variable <code>_date</code> can be either <code>NaT</code> or <code>Timestamp('2017-12-02 00:00:00')</code> </p>
  
  <p>If I use this: <code>np.isnat(np.datetime64(_date))</code>, it works for <code>Timestamp('2017-12-02 00:00:00')</code> but not <code>NaT</code> </p>