fix(c++): fix NULL type in custom op

source/api_cc/src/DeepPotPT.cc

@@ -174,6 +174,27 @@ void DeepPotPT::compute(ENERGYVTYPE& ener,
     nlist_data.padding();
     if (do_message_passing) {
       int nswap = lmp_list.nswap;
+      std::vector<std::vector<int>> sendlist_new;
+      sendlist_new.resize(nswap);
+      // select real atoms in sendlist
+      for (int s = 0; s < nswap; ++s) {
+        int cnt = 0;
+        sendlist_new[s].reserve(lmp_list.sendnum[s]);
+        for (int k = 0; k < lmp_list.sendnum[s]; ++k) {
+          const int old_idx = lmp_list.sendlist[s][k];
+          int mapped = (old_idx >= 0 && old_idx < (int)fwd_map.size())
+                           ? fwd_map[old_idx]
+                           : -1;
+          if (mapped >= 0) {
+            sendlist_new[s].push_back(mapped);
+            ++cnt;
+          }
+        }
+        std::memcpy(lmp_list.sendlist[s], sendlist_new[s].data(),
+                    cnt * sizeof(int));
+        lmp_list.sendnum[s] = cnt;
+        lmp_list.recvnum[s] = cnt;
+      }
       torch::Tensor sendproc_tensor =
           torch::from_blob(lmp_list.sendproc, {nswap}, int32_option);
       torch::Tensor recvproc_tensor =