$this->substPaths takes 2 parameters

protected function substPaths( $paths, FileBackend $backend ) {

Pass $backend from the for loop

diff --git a/includes/filerepo/backend/FileBackendMultiWrite.php b/includes/filerepo/backend/FileBackendMultiWrite.php
index 44a07be..9568207 100644 (file)
--- a/includes/filerepo/backend/FileBackendMultiWrite.php
+++ b/includes/filerepo/backend/FileBackendMultiWrite.php
@@ -392,7 +392,7 @@ class FileBackendMultiWrite extends FileBackendBase {
         */
        public function clearCache( array $paths = null ) {
                foreach ( $this->backends as $backend ) {
-                       $realPaths = is_array( $paths ) ? $this->substPaths( $paths ) : null;
+                       $realPaths = is_array( $paths ) ? $this->substPaths( $paths, $backend ) : null;
                        $backend->clearCache( $realPaths );
                }
        }