Actually validate order before use in spline

pandas/core/missing.py

@@ -293,8 +293,8 @@ def _interpolate_scipy_wrapper(x, y, new_x, method, fill_value=None,
                                     bounds_error=bounds_error)
         new_y = terp(new_x)
     elif method == 'spline':
-        # GH #10633
-        if not order:
+        # GH #10633, #24014
+        if order is None or not (0 < order):
             raise ValueError("order needs to be specified and greater than 0")
         terp = interpolate.UnivariateSpline(x, y, k=order, **kwargs)
         new_y = terp(new_x)

pandas/tests/series/test_missing.py

@@ -1336,8 +1336,9 @@ def test_spline_error(self):
             s.interpolate(method='spline')
 
         msg = "order needs to be specified and greater than 0"
-        with pytest.raises(ValueError, match=msg):
-            s.interpolate(method='spline', order=0)
+        for invalid_order in [-1, -1., 0, 0., np.nan]:
+            with pytest.raises(ValueError, match=msg):
+                s.interpolate(method='spline', order=invalid_order)
 
     def test_interp_timedelta64(self):
         # GH 6424