_find_libs_to_preserve: always return set

diff --git a/pym/portage/dbapi/vartree.py b/pym/portage/dbapi/vartree.py
index fd5c774a354a0699ee71de84a33eebe72a8f38ce..cd93a12ff11c72cfc1631bdc28cc22e6b86571f6 100644 (file)
--- a/pym/portage/dbapi/vartree.py
+++ b/pym/portage/dbapi/vartree.py
@@ -2350,7 +2350,7 @@ 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