=== modified file 'bzrlib/option.py'
--- bzrlib/option.py	
+++ bzrlib/option.py	
@@ -99,6 +99,10 @@
                 next_prefix = None
         if next_prefix is not None:
             revs.append(RevisionSpec(next_prefix))
+
+    if (len(revs) > 0) and (revs[-1].spec is None):
+        revs[-1] = RevisionSpec('-1')
+
     return revs