_find_libs_to_preserve: always return set

diff --git a/pym/portage/dbapi/vartree.py b/pym/portage/dbapi/vartree.py
index 31e1fa6cc0f23c4d2c0c3f2a0c9c5299d585b376..d0fb86c498b418d9753f7d9d51ea61b3a4884bda 100644 (file)
--- a/pym/portage/dbapi/vartree.py
+++ b/pym/portage/dbapi/vartree.py
@@ -2298,7 +2298,7 @@ class dblink(object):
                        self.vartree.dbapi._plib_registry is None or \
                        (not unmerge and self._installed_instance is None) or \
                        "preserve-libs" not in self.settings.features:
-                       return None
+                       return set()
 
                os = _os_merge
                linkmap = self.vartree.dbapi._linkmap