Fix scalar broadcast_to with nnz=0.

Fixes #513.

Author: hameerabbasi

sparse/_umath.py

@@ -274,7 +274,9 @@ def _get_expanded_coords_data(coords, data, params, broadcast_shape):
     if first_dim != -1:
         expanded_data = data[all_idx[first_dim]]
     else:
-        expanded_coords = all_idx
+        expanded_coords = (
+            all_idx if len(data) else np.empty((0, all_idx.shape[1]), dtype=np.intp)
+        )
         expanded_data = np.repeat(data, np.prod(broadcast_shape, dtype=np.int64))
         return np.asarray(expanded_coords), np.asarray(expanded_data)
 

sparse/tests/test_array_function.py

@@ -74,3 +74,8 @@ def test_property(func):
     xx = func(x)
     yy = func(y)
     assert xx == yy
+
+
+def test_broadcast_to_scalar():
+    s = sparse.COO.from_numpy([0, 0, 1, 2])
+    np.broadcast_to(np.zeros_like(s, shape=()), (3,))