[bug] fix when no package name found (#167)

* fix when no package name

* fix pre-commit style issue

* fix to ruff (legacy alias) fail test

packages/leann-core/src/leann/registry.py

@@ -33,6 +33,8 @@ def autodiscover_backends():
     discovered_backends = []
     for dist in importlib.metadata.distributions():
         dist_name = dist.metadata["name"]
+        if dist_name is None:
+            continue
         if dist_name.startswith("leann-backend-"):
             backend_module_name = dist_name.replace("-", "_")
             discovered_backends.append(backend_module_name)