test: use lammps hybrid potential to test NULL type

Signed-off-by: link89 <xuweihong.cn@gmail.com>

Author: link89

source/lmp/tests/test_lammps.py

@@ -518,9 +518,11 @@ def test_pair_deepmd_type_map(lammps_type_map) -> None:
 
 
 def test_pair_deepmd_type_map_with_null(lammps_type_map) -> None:
-    lammps_type_map.pair_style(f"deepmd {pb_file.resolve()}")
-    lammps_type_map.pair_coeff("* * H NULL")
-    lammps_type_map.run(0)
+    lammps_type_map.pair_style(
+        f"hybrid/scaled 0.5 deepmd {pb_file.resolve()} 0.5 deepmd {pb_file.resolve()}"
+    )
+    lammps_type_map.pair_coeff("* * deepmd 1 H NULL")
+    lammps_type_map.pair_coeff("* * deepmd 2 NULL O")
 
 
 def test_pair_deepmd_real(lammps_real) -> None: