Backport PR pandas-dev#51605 on branch 2.0.x (REGR: MultiIndex.isin with empty iterable raising) (pandas-dev#51617)

Backport PR pandas-dev#51605: REGR: MultiIndex.isin with empty iterable raising

Co-authored-by: Patrick Hoefler <[email protected]>

Author: meeseeksmachine

pandas/core/indexes/multi.py

@@ -3748,6 +3748,8 @@ def delete(self, loc) -> MultiIndex:
     @doc(Index.isin)
     def isin(self, values, level=None) -> npt.NDArray[np.bool_]:
         if level is None:
+            if len(values) == 0:
+                return np.zeros((len(self),), dtype=np.bool_)
             if not isinstance(values, MultiIndex):
                 values = MultiIndex.from_tuples(values)
             return values.unique().get_indexer_for(self) != -1

pandas/tests/indexes/multi/test_isin.py

@@ -85,3 +85,11 @@ def test_isin_multi_index_with_missing_value(labels, expected, level):
     midx = MultiIndex.from_arrays([[np.nan, "a", "b"], ["c", "d", np.nan]])
     result = midx.isin(labels, level=level)
     tm.assert_numpy_array_equal(result, expected)
+
+
+def test_isin_empty():
+    # GH#51599
+    midx = MultiIndex.from_arrays([[1, 2], [3, 4]])
+    result = midx.isin([])
+    expected = np.array([False, False])
+    tm.assert_numpy_array_equal(result, expected)