Backport PR #31684 on branch 1.0.x (BUG: string methods with NA)

doc/source/whatsnew/v1.0.2.rst

@@ -84,6 +84,10 @@ Bug fixes
 - Fixed bug where :meth:`GroupBy.first` and :meth:`GroupBy.last` would raise a ``TypeError`` when groups contained ``pd.NA`` in a column of object dtype (:issue:`32123`)
 - Fix bug in :meth:`Series.convert_dtypes` for series with mix of integers and strings (:issue:`32117`)
 
+**Strings**
+
+- Using ``pd.NA`` with :meth:`Series.str.repeat` now correctly outputs a null value instead of raising error for vector inputs (:issue:`31632`)
+
 .. ---------------------------------------------------------------------------
 
 .. _whatsnew_102.contributors:

pandas/core/strings.py

@@ -778,6 +778,8 @@ def scalar_rep(x):
     else:
 
         def rep(x, r):
+            if x is libmissing.NA:
+                return x
             try:
                 return bytes.__mul__(x, r)
             except TypeError:

pandas/tests/test_strings.py

@@ -1157,6 +1157,18 @@ def test_repeat(self):
         assert isinstance(rs, Series)
         tm.assert_series_equal(rs, xp)
 
+    def test_repeat_with_null(self):
+        # GH: 31632
+        values = Series(["a", None], dtype="string")
+        result = values.str.repeat([3, 4])
+        exp = Series(["aaa", None], dtype="string")
+        tm.assert_series_equal(result, exp)
+
+        values = Series(["a", "b"], dtype="string")
+        result = values.str.repeat([3, None])
+        exp = Series(["aaa", None], dtype="string")
+        tm.assert_series_equal(result, exp)
+
     def test_match(self):
         # New match behavior introduced in 0.13
         values = Series(["fooBAD__barBAD", np.nan, "foo"])