Support empty path in Nav

mkdocs_gen_files/nav.py

@@ -29,8 +29,6 @@ def __setitem__(self, keys: str | tuple[str, ...], value: str):
         if isinstance(keys, str):
             keys = (keys,)
         cur = self._data
-        if not keys:
-            raise ValueError(f"The navigation path must not be empty (got {keys!r})")
         for key in keys:
             if not isinstance(key, str):
                 raise TypeError(
@@ -43,7 +41,9 @@ def __setitem__(self, keys: str | tuple[str, ...], value: str):
 
     def items(self) -> Iterable[Item]:
         """Allows viewing the nav as a flattened sequence."""
-        return self._items(self._data, 0)
+        if None in self._data:
+            yield self.Item(level=0, title="", filename=self._data[None])
+        yield from self._items(self._data, 0)
 
     @classmethod
     def _items(cls, data: Mapping, level: int) -> Iterable[Item]:

tests/nav/test_nav_none.yml

@@ -0,0 +1,8 @@
+code: |
+  nav[()] = "index.md"
+  nav["a"] = "a/index.md"
+  nav["a", "b"] = "a/b.md"
+output: |
+  * [](index.md)
+  * [a](a/index.md)
+      * [b](a/b.md)