Revert "fix stan"

This reverts commit b0dfd1a.

src/Tokenizer.php

@@ -838,10 +838,6 @@ private function makeRegexFromList(array $values, bool $sorted = false): string
 
             $regex .= preg_quote($prefix, '/');
 
-            if (count($items) === 1) {
-                assert(reset($items) !== false);
-            }
-
             $regex .= count($items) === 1
                 ? preg_quote(substr(reset($items), strlen($prefix)), '/')
                 : $this->makeRegexFromList(array_map(static fn ($v) => substr($v, strlen($prefix)), $items), true);