Example of fpw_auto_excerpt filter in Feature a Page Widget 2.0. By default, the widget only shows the excerpt for posts with an explicitly-set excerpt (i.e. has_excerpt() is TRUE).

fpw_auto_excerpt_filter_example.php

<?php
/**
 * Set fpw_auto_excerpt to TRUE to allow auto-generated excerpts if the Excerpt field is blank
 *
 * Uses the_excerpt() and associated filters.
 */
add_filter( 'fpw_auto_excerpt', '__return_true' );