BUG: Fix construction of Categorical from pd.NA

doc/source/whatsnew/v1.0.2.rst

@@ -31,6 +31,11 @@ Bug fixes
 **Categorical**
 
 - Fixed bug where :meth:`Categorical.from_codes` improperly raised a ``ValueError`` when passed nullable integer codes. (:issue:`31779`)
+- Fixed bug where :meth:`Categorical` constructor would raise a ``TypeError`` when given a numpy array containing :class:`NA`. (:issue:`31927`)
+
+**MultiIndex**
+
+- Fixed bug where :meth:`MultiIndex.from_product` would break when handling numpy object arrays containing ``NA``. (:issue:`31883`)
 
 **I/O**
 

pandas/_libs/hashtable_class_helper.pxi.in

@@ -10,6 +10,7 @@ WARNING: DO NOT edit .pxi FILE directly, .pxi is generated from .pxi.in
 # ----------------------------------------------------------------------
 
 from pandas._libs.tslibs.util cimport get_c_string
+from pandas._libs.missing cimport C_NA
 
 {{py:
 
@@ -1032,8 +1033,12 @@ cdef class PyObjectHashTable(HashTable):
             val = values[i]
             hash(val)
 
-            if ignore_na and ((val != val or val is None)
-                              or (use_na_value and val == na_value)):
+            if ignore_na and (
+                (val is C_NA)
+                or (val != val)
+                or (val is None)
+                or (use_na_value and val == na_value)
+            ):
                 # if missing values do not count as unique values (i.e. if
                 # ignore_na is True), skip the hashtable entry for them, and
                 # replace the corresponding label with na_sentinel

pandas/tests/arrays/categorical/test_constructors.py

@@ -458,6 +458,14 @@ def test_constructor_with_categorical_categories(self):
         result = Categorical(["a", "b"], categories=CategoricalIndex(["a", "b", "c"]))
         tm.assert_categorical_equal(result, expected)
 
+    def test_construction_with_null(self, nulls_fixture):
+        # https://github.com/pandas-dev/pandas/issues/31927
+        values = ["a", nulls_fixture, "b"]
+        result = Categorical(np.array(values, dtype=object))
+        expected = Categorical(values)
+
+        tm.assert_categorical_equal(result, expected)
+
     def test_from_codes(self):
 
         # too few categories

pandas/tests/indexing/multiindex/test_multiindex.py

@@ -111,3 +111,13 @@ def test_nested_tuples_duplicates(self):
         df3 = df.copy(deep=True)
         df3.loc[[(dti[0], "a")], "c2"] = 1.0
         tm.assert_frame_equal(df3, expected)
+
+    def test_multiindex_from_product_contains_na(self):
+        # https://github.com/pandas-dev/pandas/issues/31883
+        values = [np.array([0.0, pd.NA], dtype="object"), ["a", "b"]]
+        tuples = [(0.0, "a"), (0.0, "b"), (np.nan, "a"), (np.nan, "b")]
+
+        result = pd.MultiIndex.from_product(values)
+        expected = pd.MultiIndex.from_tuples(tuples)
+
+        tm.assert_index_equal(result, expected)