Correct the return type.

Author: Julian

referencing/_core.py

@@ -258,7 +258,7 @@ def pointer(self, pointer: str, resolver: Resolver[D]) -> Resolved[D]:
 
         """
         if not pointer:
-            return self
+            return Resolved(contents=self.contents, resolver=resolver)
 
         contents = self.contents
         segments: list[int | str] = []