mercurial/hg.py

--- a/mercurial/hg.py	Tue Jun 28 03:08:47 2005 -0800
+++ b/mercurial/hg.py	Tue Jun 28 10:42:02 2005 -0800
@@ -917,6 +917,9 @@
             if f in m:
                 raise RepoError("already have changeset " + short(f[:4]))
 
+        if fetch == [nullid]:
+            raise RepoError("unrelated repository")
+
         self.ui.note("adding new changesets starting at " +
                      " ".join([short(f) for f in fetch]) + "\n")