Is it possible to combine if_not_exists and list_append in update_item : <p>I'm trying to use the <code>update_item</code> functionality for DynamoDB in boto3. </p>

<p>I'm struggling right now to update lists for items. I would like to create a new list if the list does not exist yet and otherwise append to the existing list. </p>

<p>Using an <code>UpdateExpression</code> of the form <code>SET my_list = list_append(my_list, :my_value)</code> returns an error <em>"The provided expression refers to an attribute that does not exist in the item"</em> if the list does not exist yet.</p>

<p>Any idea how I would have to modify my <code>UpdateExpression</code>?</p>

<p>Thanks &amp; best regards,
Fabian</p>
