Skip redundant enif_is_empty_list checks during encode

enif_get_list_cell fails when the list is empty.

c_src/encoder.c

@@ -740,17 +740,13 @@ encode_iter(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
         if(enif_is_identical(curr, e->atoms->ref_object)) {
             curr = termstack_pop(&stack);
 
-            if(enif_is_empty_list(env, curr)) {
+            if(!enif_get_list_cell(env, curr, &item, &curr)) {
                 if(!enc_end_object(e)) {
                     ret = enc_error(e, "internal_error");
                     goto done;
                 }
                 continue;
             }
-            if(!enif_get_list_cell(env, curr, &item, &curr)) {
-                ret = enc_error(e, "internal_error");
-                goto done;
-            }
             if(!enif_get_tuple(env, item, &arity, &tuple)) {
                 ret = enc_obj_error(e, "invalid_object_member", item);
                 goto done;
@@ -778,7 +774,7 @@ encode_iter(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
         } else if(enif_is_identical(curr, e->atoms->ref_array)) {
             curr = termstack_pop(&stack);
 
-            if(enif_is_empty_list(env, curr)) {
+            if(!enif_get_list_cell(env, curr, &item, &curr)) {
                 if(!enc_end_array(e)) {
                     ret = enc_error(e, "internal_error");
                     goto done;
@@ -789,10 +785,6 @@ encode_iter(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
                 ret = enc_error(e, "internal_error");
                 goto done;
             }
-            if(!enif_get_list_cell(env, curr, &item, &curr)) {
-                ret = enc_error(e, "internal_error");
-                goto done;
-            }
 
             termstack_push(&stack, curr);
             termstack_push(&stack, e->atoms->ref_array);
@@ -850,17 +842,13 @@ encode_iter(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
                 ret = enc_error(e, "internal_error");
                 goto done;
             }
-            if(enif_is_empty_list(env, tuple[0])) {
+            if(!enif_get_list_cell(env, tuple[0], &item, &curr)) {
                 if(!enc_end_object(e)) {
                     ret = enc_error(e, "internal_error");
                     goto done;
                 }
                 continue;
             }
-            if(!enif_get_list_cell(env, tuple[0], &item, &curr)) {
-                ret = enc_error(e, "internal_error");
-                goto done;
-            }
             if(!enif_get_tuple(env, item, &arity, &tuple)) {
                 ret = enc_obj_error(e, "invalid_object_member", item);
                 goto done;
@@ -895,17 +883,14 @@ encode_iter(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
                 ret = enc_error(e, "internal_error");
                 goto done;
             }
-            if(enif_is_empty_list(env, curr)) {
+
+            if(!enif_get_list_cell(env, curr, &item, &curr)) {
                 if(!enc_end_array(e)) {
                     ret = enc_error(e, "internal_error");
                     goto done;
                 }
                 continue;
             }
-            if(!enif_get_list_cell(env, curr, &item, &curr)) {
-                ret = enc_error(e, "internal_error");
-                goto done;
-            }
 
             termstack_push(&stack, curr);
             termstack_push(&stack, e->atoms->ref_array);