BUG: Allow empty interesection in DataFrame.update

Author: rhshadrach

pandas/core/frame.py

@@ -10081,12 +10081,6 @@ def update(
             raise ValueError("Update not allowed with duplicate indexes on other.")
 
         index_intersection = other.index.intersection(self.index)
-        if index_intersection.empty:
-            raise ValueError(
-                "Update not allowed when the index on `other` has no intersection "
-                "with this dataframe."
-            )
-
         other = other.reindex(index_intersection)
         this_data = self.loc[index_intersection]
 

pandas/tests/frame/methods/test_update.py

@@ -215,13 +215,6 @@ def test_update_raises_on_duplicate_argument_index(self):
         with pytest.raises(ValueError, match="duplicate index"):
             df.update(other)
 
-    def test_update_raises_without_intersection(self):
-        # GH#55509
-        df = DataFrame({"a": [1]}, index=[1])
-        other = DataFrame({"a": [2]}, index=[2])
-        with pytest.raises(ValueError, match="no intersection"):
-            df.update(other)
-
     def test_update_on_duplicate_frame_unique_argument_index(self):
         # GH#55509
         df = DataFrame({"a": [1, 1, 1]}, index=[1, 1, 2], dtype=np.dtype("intc"))