Handle empty pointers (root pointers) in Resource.pointer.

Resource.lookup did this correctly for fragment-represented pointers,
but this function needs to as well.

Closes: #148

docs/changes.rst

@@ -2,6 +2,12 @@
 Changelog
 =========
 
+v0.35.1
+-------
+
+* Make ``Resource.pointer`` also properly handle empty pointers (which refer to the root document).
+  This fix likely only affects you if you were using that function directly, as ``Resource.lookup`` already handles empty fragments.
+
 v0.35.0
 -------
 

referencing/_core.py

@@ -257,6 +257,9 @@ def pointer(self, pointer: str, resolver: Resolver[D]) -> Resolved[D]:
                 if the pointer points to a location not present in the document
 
         """
+        if not pointer:
+            return self
+
         contents = self.contents
         segments: list[int | str] = []
         for segment in unquote(pointer[1:]).split("/"):

referencing/tests/test_core.py

@@ -681,6 +681,12 @@ def test_pointer_to_array(self):
         resolver = Registry().resolver()
         assert resource.pointer("/foo/bar/0", resolver=resolver).contents == 3
 
+    def test_root_pointer(self):
+        contents = {"foo": "baz"}
+        resource = Resource.opaque(contents=contents)
+        resolver = Registry().resolver()
+        assert resource.pointer("", resolver=resolver).contents == contents
+
     def test_opaque(self):
         contents = {"foo": "bar"}
         assert Resource.opaque(contents) == Resource(