TextArea and RichTextArea fields cause a warning in PHP 8.1

[matthewmcvickar]

Description of the bug

Empty FieldManager_TextArea fields (e.g., ones on new post pages, or ones that have never been given a value) show a warning in PHP 8.1+.

This appears to be happening because esc_textarea() is run on the value when rendering the textarea, and the esc_textarea() function uses htmlspecialchars(), and htmlspecialchars() no longer accepts null without a warning as of PHP 8.1.

A workaround: if the FieldManager_TextArea is initiated with a default_value set to '' (empty string), this warning does not happen, presumably because then the htmlspecialchars() function runs on an empty string instead of null.

Steps To Reproduce

1. Configure a field manager with a textarea field, like this example adapted from the FieldManager homepage:

   add_action( 'fm_post_post', function() {
     $fm = new Fieldmanager_Group( array(
       'name' => 'contact_information',
       'children' => array(
         'name' => new Fieldmanager_TextField( 'Name' ),
         'description' => new Fieldmanager_TextArea( 'Description' ),
       ),
     ) );
     $fm->add_meta_box( 'Contact Information', 'post' );
   } );
   

2. Load the page in an environment running PHP 8.1.

3. Notice the error in the PHP error log:

   PHP Deprecated:  htmlspecialchars(): Passing null to parameter #1 ($string) of type string is deprecated in /wp/wp-includes/formatting.php on line 4732
   

Additional Information

When I created this ticket, I thought this warning was only happening for textareas in repeatable groups, but it actually applies to all textareas.

[matthewmcvickar]

It appears this issue was fixed via https://github.com/alleyinteractive/wordpress-fieldmanager/pull/866 (see file diff), and so I'm going to close it.