From 16a04b61e972b1080ff4f4bf57475dc844e0614a Mon Sep 17 00:00:00 2001
From: NagIzaazShaik <176337212+shaikn6@users.noreply.github.com>
Date: Wed, 9 Sep 2026 15:02:26 -0400
Subject: [PATCH] Accept target_values=None in surface_distance trio (#3712)

surface_distance, surface_allocation and surface_direction declared
target_values: list = [] while proximity, allocation, direction and
cost_distance use None and normalize to [] in the body. Passing
target_values=None (common when wrapper code threads an optional arg
through) reached np.asarray(None) and failed before the numba kernel.

Change the three signatures to None and add the sibling
'if target_values is None: target_values = []' guard in the shared
_compute dispatcher. [] and None both mean 'every non-zero finite pixel
is a source', so callers passing an explicit list are unaffected. Also
removes the mutable default argument the siblings already avoid.
---
 xrspatial/surface_distance.py            |  9 ++++++---
 xrspatial/tests/test_surface_distance.py | 10 ++++++++++
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/xrspatial/surface_distance.py b/xrspatial/surface_distance.py
index dd2bf33b7..fcb46cb19 100644
--- a/xrspatial/surface_distance.py
+++ b/xrspatial/surface_distance.py
@@ -1383,6 +1383,9 @@ def _compute(raster, elevation, x, y, target_values, max_distance,
     signed_cellsize_x = cellsize_x * _coord_step_sign(raster, x)
     signed_cellsize_y = cellsize_y * _coord_step_sign(raster, y)
 
+    if target_values is None:
+        target_values = []
+
     target_values = np.asarray(target_values, dtype=np.float64)
     if target_values.ndim != 1:
         raise ValueError(
@@ -1528,7 +1531,7 @@ def surface_distance(
     elevation: xr.DataArray,
     x: str = "x",
     y: str = "y",
-    target_values: list = [],
+    target_values: list = None,
     max_distance: float = np.inf,
     connectivity: int = 8,
     method: str = 'planar',
@@ -1584,7 +1587,7 @@ def surface_allocation(
     elevation: xr.DataArray,
     x: str = "x",
     y: str = "y",
-    target_values: list = [],
+    target_values: list = None,
     max_distance: float = np.inf,
     connectivity: int = 8,
     method: str = 'planar',
@@ -1621,7 +1624,7 @@ def surface_direction(
     elevation: xr.DataArray,
     x: str = "x",
     y: str = "y",
-    target_values: list = [],
+    target_values: list = None,
     max_distance: float = np.inf,
     connectivity: int = 8,
     method: str = 'planar',
diff --git a/xrspatial/tests/test_surface_distance.py b/xrspatial/tests/test_surface_distance.py
index 499b689ea..b925215c5 100644
--- a/xrspatial/tests/test_surface_distance.py
+++ b/xrspatial/tests/test_surface_distance.py
@@ -613,6 +613,16 @@ def test_invalid_target_values_shape(bad):
         surface_distance(source, elev, target_values=bad)
 
 
+@pytest.mark.parametrize("func", [surface_distance, surface_allocation, surface_direction])
+def test_target_values_none_matches_empty(func):
+    """target_values=None must behave like the [] default (issue #3712)."""
+    source = _make_raster(np.array([[0.0, 1.0, 0.0, 2.0, 0.0]], dtype=np.float64))
+    elev = _make_raster(np.zeros((1, 5), dtype=np.float64))
+    expected = _compute(func(source, elev))
+    got = _compute(func(source, elev, target_values=None))
+    np.testing.assert_array_equal(np.asarray(got), np.asarray(expected))
+
+
 # ---------------------------------------------------------------------------
 # Tests — dask-specific
 # ---------------------------------------------------------------------------