1 files changed, 3 insertions, 3 deletions

diff --git a/project.py b/project.py
index 41606442..b65cb1ae 100644
--- a/project.py
+++ b/project.py
@@ -554,7 +554,7 @@ class Project:
         revisionExpr,
         revisionId,
         rebase=True,
-        groups=None,
+        groups=set(),
         sync_c=False,
         sync_s=False,
         sync_tags=True,
@@ -839,9 +839,9 @@ class Project:
         """
         default_groups = self.manifest.default_groups or ["default"]
         expanded_manifest_groups = manifest_groups or default_groups
-        expanded_project_groups = ["all"] + (self.groups or [])
+        expanded_project_groups = {"all"} | self.groups
         if "notdefault" not in expanded_project_groups:
-            expanded_project_groups += ["default"]
+            expanded_project_groups |= {"default"}
 
         matched = False
         for group in expanded_manifest_groups: