Update sphinx/domains/cpp.py

Co-authored-by: Jakob Lykke Andersen <jakobandersen@users.noreply.github.com>

sphinx/domains/cpp.py

@@ -3403,7 +3403,7 @@ def __init__(self, name: ASTNestedName, scoped: str,
         self.name = name
         self.scoped = scoped
         self.underlyingType = underlyingType
-        self.attrs = attrs or []
+        self.attrs = attrs
 
     def get_id(self, version: int, objectType: str, symbol: "Symbol") -> str:
         if version == 1: