Added code snippet to documentation to describe handling null values with date filter

doc/filters/date.rst

@@ -56,3 +56,10 @@ The default timezone can also be set globally by calling ``setTimezone()``:
 .. _`date`:         http://www.php.net/date
 .. _`DateTime`:     http://www.php.net/DateTime
 .. _`DateInterval`: http://www.php.net/DateInterval
+
+If the value passed to the ``date`` filter is null, it will return the current date by default.
+If an empty string is desired instead of the current date, use a ternary operator:
+
+.. code-block:: jinja
+
+    {{ post.published_at is empty ? "" : post.published_at|date("m/d/Y") }}