#3043779 "Source path has to start with a slash" exception when hitting path...

#3043779 "Source path has to start with a slash" exception when hitting path prefixed with index.php with RequestPath condition

core/modules/path_alias/src/AliasManager.php

@@ -146,7 +146,7 @@ public function getPathByAlias($alias, $langcode = NULL) {
   public function getAliasByPath($path, $langcode = NULL) {
     // Check the path whitelist, if the top-level part before the first /
     // then other add other checks.
-    if ($this->whitelist->get(strtok(trim($path, '/'), '/')) && (isset($path[0]) && $path[0] !== '/')) {
+    if ($this->pathPrefixes->get(strtok(trim($path, '/'), '/')) && (isset($path[0]) && $path[0] !== '/')) {
       throw new \InvalidArgumentException(sprintf('Source path %s has to start with a slash.', $path));
     }
     // If no language is explicitly specified we default to the current URL