diff --git a/hgext/beautifygraph.py b/hgext/beautifygraph.py
--- a/hgext/beautifygraph.py
+++ b/hgext/beautifygraph.py
@@ -80,6 +80,9 @@ def outputprettygraph(orig, ui, graph, *
     return orig(ui, graph, *args, **kwargs)
 
 def extsetup(ui):
+    if ui.plain('graph'):
+        return
+
     if encoding.encoding != 'UTF-8':
         ui.warn(_('beautifygraph: unsupported encoding, UTF-8 required\n'))
         return
@@ -89,8 +92,5 @@ def extsetup(ui):
                   'monospace narrow text required\n'))
         return
 
-    if ui.plain('graph'):
-        return
-
     extensions.wrapfunction(graphmod, 'outputgraph', outputprettygraph)
     extensions.wrapfunction(templatekw, 'getgraphnode', getprettygraphnode)
diff --git a/mercurial/phases.py b/mercurial/phases.py
--- a/mercurial/phases.py
+++ b/mercurial/phases.py
@@ -673,13 +673,11 @@ def newheads(repo, heads, roots):
     rev = cl.nodemap.get
     if not roots:
         return heads
-    if not heads or heads == [nullrev]:
+    if not heads or heads == [nullid]:
         return []
     # The logic operated on revisions, convert arguments early for convenience
     new_heads = set(rev(n) for n in heads if n != nullid)
     roots = [rev(n) for n in roots]
-    if not heads or not roots:
-        return heads
     # compute the area we need to remove
     affected_zone = repo.revs("(%ld::%ld)", roots, new_heads)
     # heads in the area are no longer heads