Undefined $options when there are no content types

This is a bit of an edge case, but an easy fix. In user_stats.admin.inc, Line 41, we have:

'#options' => $options,

Instead, we should be using:

'#options' => isset($options) ? $options : array(),

$options can be undefined if node_type_get_types() returns no available content types. In this case, we'll receive a PHP warning.