When updating a post, user, or term, ensure specific fields have a blank entry in the database even when null.

wp-metadata-fill-missing.php

<?php

/**
 * When updating a post, user, or term, ensure specific fields have a blank entry in the database even when null.
 *
 * @param $object_id
 * @param null $type
 * @param null $subtype
 */
function rs_insert_missing_meta_keys_on_save( $object_id, $type = null, $subtype = null ) {
	if ( $type === null ) return;
	
	$required = array(
		'post' => array(
      
      // Post type "evaluation" => post meta
			'facilitator' => array(
				'_thumbnail_id',
				'first_name',
				'last_name',
				'business_zip',
				'business_country',
				'program',
			),
      
      // Post type "evaluation" => post meta
			'evaluation' => array(
				'enable_assessments',
				'prework_status',
				'prework_end_date',
				'prework_end_sent',
			),
		),
		
		'term' => array(
      
      // Taxonomy "account-menu" => term meta
			'account-menu' => array(
				    'conditions',
				    'conditions_program',
				    'conditions_rs_status',
				    'conditions_training_date',
				    'conditions_training_date_start',
				    'conditions_training_date_end',
				    'conditions_assigned_event',
				    'conditions_role',
				),
		),
		
		'user' => array(
      // User metadata (untested)
			// 'example',
			// 'example_2',
		),
	);
	
	// Get the meta keys that we'll be checking
	if ( $type == 'post' ) {
		// Post, by post type
		$keys = isset($required['post'][$subtype]) ? $required['post'][$subtype] : false;
		
	}else if ( $type == 'term' ) {
		// Term, by taxonomy
		$keys = isset($required['term'][$subtype]) ? $required['term'][$subtype] : false;
		
	}else if ( $type == 'user' ) {
		// Users
		$keys = $required['user'];
		
	}else{
		return;
	}
	
	if ( $keys ) {
		
		// Get the current meta keys
		$meta = get_metadata( $type, $object_id );
		
		// Check if each key is present, if not then create it
		foreach( $keys as $key ) {
			if ( !isset($meta[$key]) ) {
				update_metadata( $type, $object_id, $key, '' );
			}
		}
		
	}
}
add_action( 'save_post',      function( $post_id )                    { rs_insert_missing_meta_keys_on_save($post_id, 'post', get_post_type($post_id));  }, 1, 1 );
add_action( 'profile_update', function( $user_id )                    { rs_insert_missing_meta_keys_on_save($user_id, 'user');                                      }, 1, 2 );
add_action( 'edited_term',    function( $term_id, $tt_id, $taxonomy ) { rs_insert_missing_meta_keys_on_save($term_id, 'term', $taxonomy);                    }, 1, 3 );

// https://rsjan2022.wpengine.com/?rs_bulk_insert_missing_taxonomy_metadata
function rs_bulk_insert_missing_taxonomy_metadata() {
	if ( ! current_user_can('administrator') ) wp_die('admin only in ' . __FILE__);
	
	// Loop through all items in a taxonomy and fill meta keys that are missing
	$taxonomies = array(
		'account-menu',
	);
	
	$terms = get_terms(array( 'taxonomy' => $taxonomies, 'hide_empty' => false ));
	
	echo '<pre>';
	echo "Filling keys for these terms:\n\n";
	
	foreach( $terms as $i => $term ) {
		echo "[$term->taxonomy][$term->term_id] \"$term->name\"" . "\n";
		
		$before = get_term_meta( $term->term_id );
		
		// Uses the same action as from wp-includes/taxonomy.php.
		// This way we know it works normally - when terms are edited.
		/**
		 * @param int    $term_id  Term ID.
		 * @param int    $tt_id    Term taxonomy ID.
		 * @param string $taxonomy Taxonomy slug.
		 */
		do_action( 'edited_term', $term->term_id, $term->term_taxonomy_id, $term->taxonomy );
		
		// needed for $after to get new values
		clean_term_cache( $term->term_id );
		clean_object_term_cache( $term->term_id, $term->taxonomy );
		
		$after = get_term_meta( $term->term_id );
		
		$diff = count($after) - count($before);
		
		echo "   ";
		if ( $diff === 0 ) {
			echo "No changes";
		}else if ( $diff === 1 ) {
			echo "1 change";
		}else {
			echo $diff . " changes";
		}
		echo "\n";
		echo "\n";
	}
	
	exit;
}
if ( isset($_GET['rs_bulk_insert_missing_taxonomy_metadata']) ) add_action( 'init', 'rs_bulk_insert_missing_taxonomy_metadata' );