Fatal error: Class 'OptionLicenses' not found in … option-licenses.php on line

After upgrading from WPSOLR 8.6 to 9.1 we get a blank admin page and (after turning on debugging) this error:

Fatal error: Class ‘OptionLicenses’ not found in [site root]/wp-content/plugins/wpsolr-search-engine/classes/extensions/licenses/option-licenses.php on line 4

We note that this file did not exist in version 8.6.

The first few lines of option-licenses.php are:

<?php

// Register Ajax events
add_action( 'wp_ajax_' . OptionLicenses::AJAX_ACTIVATE_LICENCE, array(
        'OptionLicenses',
        OptionLicenses::AJAX_ACTIVATE_LICENCE
) );

The file is called from /wp-content/plugins/wpsolr-search-engine/classes/extensions/wpsolr-extensions.php.

Running diff of 8.6 against 9.2 shows:

< 	static $wpsolr_extensions;
69,71d67
< 	// Option: licenses
< 	const OPTION_LICENSES = 'Licenses';
<
207,218d202
< 			),
< 		self::OPTION_LICENSES             =>
< 			array(
< 				self::_CONFIG_EXTENSION_CLASS_NAME              => 'OptionLicenses',
< 				self::_CONFIG_PLUGIN_CLASS_NAME                 => 'OptionLicenses',
< 				self::_CONFIG_EXTENSION_DIRECTORY               => 'licenses/',
< 				self::_CONFIG_EXTENSION_FILE_PATH               => 'licenses/option-licenses.php',
< 				self::_CONFIG_EXTENSION_ADMIN_OPTIONS_FILE_PATH => 'licenses/admin_options.inc.php',
< 				self::_CONFIG_OPTIONS                           => array(
< 					self::_CONFIG_OPTIONS_DATA                 => 'wpsolr_licenses',
< 					self::_CONFIG_OPTIONS_IS_ACTIVE_FIELD_NAME => 'is_extension_active'
< 				)
232,236c216
<
< 		if ( ! isset( static::$wpsolr_extensions ) ) {
<
< 			static::$wpsolr_extensions = new self();
< 		}
---
> 		$wpsolr_extensions = new self();

Clearly, there’s something we’re missing. Any help steering us in the right direction would be much appreciated!

PS – We Googled and searched this support forum without finding help on this…probably missed something somewhere, apologies in advance!

https://www.ads-software.com/plugins/wpsolr-search-engine/