X "B:" indicates ø bucket with k&b, "B" - ø bucket with only keys

wcfs/internal/xbtree.py

@@ -187,6 +187,9 @@ class Bucket(object):
             kvv = ['%s' % k for k in b.keyv]
         else:
             assert len(b.keyv) == len(b.valuev)
+            if len(b.keyv) == 0:
+                kvv = [':']
+            else:
                 kvv = ['%s:%s' % (k,v) for (k,v) in zip(b.keyv, b.valuev)]
         return "B" + ','.join(kvv)
     __repr__ = __str__
@@ -762,7 +765,10 @@ def TopoEncode(tree, vencode=lambda v: '%d' % v):
             tnode = ('T' if isinstance(node, Tree) else 'B')
             if isinstance(node, Bucket) and node.valuev is not None:
                 # bucket with key and values
-                assert len(node.valuev) == len(node.keyv)
+                assert len(node.keyv) == len(node.valuev)
+                if len(node.keyv) == 0:
+                    tnode += ':'
+                else:
                     vtxtv = []
                     for v in node.valuev:
                         vtxt = vencode(v)
@@ -820,6 +826,7 @@ def TopoDecode(text, vdecode=int):
             withV = (typ is Bucket and ':' in tkeys)
             keyv  = []
             valuev= [] if withV else None
+            if tkeys != ':': # "B:" indicates ø bucket with values
                 for tkey in tkeyv:
                     ktxt = tkey
                     if withV: