Update _reloader.py

root={}
path=()
os.path.join(*path)
Traceback (most recent call last):
  File "<string>", line 1, in <module>
TypeError: join() missing 1 required positional argument: 'path'

CHANGES.rst

@@ -5,6 +5,8 @@ Version 3.0.3
 
 Unreleased
 
+-   Make reloader more robust when ``""`` is in ``sys.path``. :pr:`2823`
+
 
 Version 3.0.2
 -------------

src/werkzeug/_reloader.py

@@ -157,7 +157,9 @@ def _walk(node: t.Mapping[str, dict[str, t.Any]], path: tuple[str, ...]) -> None
         for prefix, child in node.items():
             _walk(child, path + (prefix,))
 
-        if not node:
+        # If there are no more nodes, and a path has been accumulated, add it.
+        # Path may be empty if the "" entry is in sys.path.
+        if not node and path:
             rv.add(os.path.join(*path))
 
     _walk(root, ())