[WordPress Plugin] Copy ACF field to Post Excerpt

acf-to-excerpt.php

<?php
/**
 * Plugin Name: ACF Field to Excerpt
 * Plugin URI: http://wordpress.stackexchange.com/q/70990/12615
 */

function acf_to_excerpt(){
    $post_type = 'post';
    $field = 'summary';
    
    $args = array( 
        'post_type'   => $post_type,
        'numberposts' => -1
    );
    
    $posts = get_posts( $args );

    foreach ( $posts as $post ){
        
        if ( $post->post_excerpt === '' ) {
            
            $content = get_field( $field, $post->ID, false );
            
            if ( $content !== '' ) {
                $updated_post                 = [];
                $updated_post                 = get_post( $post->ID, 'ARRAY_A' );
                $updated_post['post_excerpt'] = $content;
                wp_update_post($updated_post);
            }
        }
    }   
}

register_activation_hook( __FILE__, 'acf_to_excerpt' );