title: In Dynamoose, how to specify schema for field that allows either String or NULL?
body: <p>I'm trying to define the schema for a field that will either be a string value or NULL.</p>
  <p>From what I can tell, this should work:</p>
  <pre class="lang-js prettyprint-override"><code>myField: [String, dynamoose.type.NULL]
  </code></pre>
  <p>However, when it encounters a <code>null</code> value in the table, I get the following error:</p>
  <pre><code>TypeMismatch: Expected example.myField to be of type string, instead found type null.
  </code></pre>
  <p>The only thing I've found that works is setting the field to <code>dynamoose.type.ANY</code>, which seems like it defeats the purpose of defining the field at all.</p>