RepositoryDir.file_get_contents(): return values

- false=access denied
- null=does not exist

src/RepositoryDir.php

@@ -82,13 +82,17 @@ class RepositoryDir extends RepositoryBase {
 
   function file_get_contents ($file) {
     if (substr($file, 0, 1) === '.' || preg_match("/\/\./", $file)) {
-      return null;
+      return false;
     }
 
     if (!$this->access($file)) {
       return false;
     }
 
+    if (!file_exists("{$this->path}/{$file}")) {
+      return null;
+    }
+
     return file_get_contents("{$this->path}/{$file}");
   }