diff --git a/mercurial/debugcommands.py b/mercurial/debugcommands.py
--- a/mercurial/debugcommands.py
+++ b/mercurial/debugcommands.py
@@ -2752,7 +2752,14 @@
 
             args = {}
             for line in lines:
-                key, value = line.lstrip().split(' ', 1)
+                # We need to allow empty values.
+                fields = line.lstrip().split(' ', 1)
+                if len(fields) == 1:
+                    key = fields[0]
+                    value = ''
+                else:
+                    key, value = fields
+
                 args[key] = ast.literal_eval(b'b"%s"' % value)
 
             if batchedcommands is not None: