sgf_meta_fields.php

<?php
function sgf_meta_fields() {
	$fields_array = apply_filters( 'sgf_register_fields', [] );
	foreach ( $fields_array as $field ) {
		// Ensure post type exists and field name is valid
		if ( ! $field['post_type'] || ! post_type_exists( $field['post_type'] ) || ! $field['meta_key'] || ! is_string( $field['meta_key'] ) ) {
			return;
		}

		// Using Null Coalesce Operator to set defaults
		register_post_meta( $field['post_type'], $field['meta_key'], [
			'type'         => $field['type'] ?? 'string',
			'single'       => $field['single'] ?? true,
			'default'      => $field['default'] ?? '',
			'show_in_rest' => $field['show_in_rest'] ?? true,
			'control'      => $field['control'] ?? 'text'
		] );
	}

}

add_action( 'rest_api_init', 'sgf_meta_fields' , 0);