Allow projects with groups=None

Mirror manifest and repo projects are outside the manifest and
have no groups.  Allow project groups to be None for these

Change-Id: I3e1c4add894fe1c43aa4e77a1fc1558aa10dd191
diff --git a/ b/
index afab1b7..4f0345f 100644
--- a/
+++ b/
@@ -666,6 +666,8 @@
        manifest_groups: "-group1,group2"
        the project will be matched.
+    if self.groups is None:
+      return True
     matched = False
     for group in manifest_groups:
       if group.startswith('-') and group[1:] in self.groups: