Update src/wp-admin/includes/class-wp-automatic-updater.php

Co-authored-by: Weston Ruter <westonruter@gmail.com>

Author: tlloancy

src/wp-admin/includes/class-wp-automatic-updater.php

@@ -1542,7 +1542,7 @@ protected function send_plugin_theme_email( $type, $successful_updates, $failed_
 
 		if ( WP_DEBUG && ( 'fail' === $type || 'mixed' === $type ) ) {
 			$fatal_error = get_transient( 'wp_updater_last_fatal_error' );
-			if ( $fatal_error ) {
+			if ( is_string( $fatal_error ) ) {
 				$email['body'] .= "\n\n=== " . __( 'Last fatal PHP error', 'default' ) . " ===\n";
 				$email['body'] .= '• ' . $fatal_error . "\n";
 				$email['body'] .= "========================================\n";