dev#189214: Add managed libraries select in users edit/add form

library/Class/Users.php

@@ -585,7 +585,7 @@ class Class_Users extends Storm_Model_Abstract {
 
   public function canManageLibrary($library): bool
   {
-    return in_array($library->getId(), $this->managedLibraries())
+    return ($library && in_array($library->getId(), $this->managedLibraries()))
       ? true
       : false;
   }