diff --git a/bumpversion/__init__.py b/bumpversion/__init__.py
index 29da2a2..5884a16 100644
--- a/bumpversion/__init__.py
+++ b/bumpversion/__init__.py
@@ -440,7 +440,11 @@ def __init__(self, parse, serialize, search, replace, part_configs=None):
         self.replace = replace
 
     def _labels_for_format(self, serialize_format):
-        return (label for _, label, _, _ in Formatter().parse(serialize_format))
+        return (
+            label
+            for _, label, _, _ in Formatter().parse(serialize_format)
+            if label
+        )
 
     def order(self):
         # currently, order depends on the first given serialization format