diff --git a/fastapi_cache/__init__.py b/fastapi_cache/__init__.py
index b5f9218..eda2762 100644
--- a/fastapi_cache/__init__.py
+++ b/fastapi_cache/__init__.py
@@ -108,5 +108,5 @@ async def clear(
         assert (  # noqa: S101
             cls._backend and cls._prefix is not None
         ), "You must call init first!"
-        namespace = cls._prefix + (":" + namespace if namespace else "")
+        namespace = f"{cls._prefix}:{namespace}" if namespace else None
         return await cls._backend.clear(namespace, key)