revlog: always add the magic nullid/nullrev entry in parseindex

mercurial/revlog.py

@@ -143,6 +143,9 b' class revlogoldio(object):'
             nodemap[e[6]] = n
             n += 1
 
+        # add the magic null revision at -1
+        index.append((0, 0, 0, -1, -1, -1, -1, nullid))
+
         return index, nodemap, None
 
     def packentry(self, entry, node, version, rev):
@@ -262,7 +265,6 b' class revlog(object):'
         self._io = revlogio()
         if self.version == REVLOGV0:
             self._io = revlogoldio()
-        if i:
             try:
                 d = self._io.parseindex(i, self._inline)
             except (ValueError, IndexError):
@@ -273,10 +275,6 b' class revlog(object):'
             if not self._chunkcache:
                 self._chunkclear()
 
-        # add the magic null revision at -1 (if it hasn't been done already)
-        if self.index == [] or self.index[-1][7] != nullid:
-            self.index.append((0, 0, 0, -1, -1, -1, -1, nullid))
-
     @util.propertycache
     def nodemap(self):
         n = {nullid: nullrev}