kmx.io/rbpkg

diff --git a/lib/rbpkg.rb b/lib/rbpkg.rb
index 16871b5..1990e27 100644
--- a/lib/rbpkg.rb
+++ b/lib/rbpkg.rb
@@ -461,7 +461,7 @@ EOF
 
   def self.upgrade(repo, tree)
     upgrade_self
-    Repos.repo(repo, tree).upgrade()
+    Repos.repo(repo, tree).upgrade() if repo
   end
 
   def self.upgrade_self