diff --git a/src/core/manager_internal.c b/src/core/manager_internal.c
index 3e10dc15..0f9353f4 100644
--- a/src/core/manager_internal.c
+++ b/src/core/manager_internal.c
@@ -243,9 +243,11 @@ int neu_manager_subscribe(neu_manager_t *manager, const char *app,
     // guard against empty mqtt topic parameter
     // this is not an elegant solution due to the current architecture
     if (params && 0 == strcmp(adapter->module->module_name, "MQTT")) {
-        neu_json_elem_t elem = { .name = "topic", .t = NEU_JSON_STR };
-        neu_parse_param(params, NULL, 1, &elem);
-        if (elem.v.val_str && 0 == strlen(elem.v.val_str)) {
+        neu_json_elem_t elem = { .name      = "topic",
+                                 .t         = NEU_JSON_STR,
+                                 .v.val_str = NULL };
+        int             ret  = neu_parse_param(params, NULL, 1, &elem);
+        if (ret != 0 || (elem.v.val_str && 0 == strlen(elem.v.val_str))) {
             free(elem.v.val_str);
             return NEU_ERR_MQTT_SUBSCRIBE_FAILURE;
         }
diff --git a/tests/ft/neuron/api.py b/tests/ft/neuron/api.py
index 23f1bf9e..6616ee76 100644
--- a/tests/ft/neuron/api.py
+++ b/tests/ft/neuron/api.py
@@ -247,12 +247,12 @@ def get_subscribe_group(app, driver=None, group=None):
 
 
 @gen_check
-def subscribe_group(app, driver, group, params={}):
+def subscribe_group(app, driver, group, params={"topic": "/neuron/mqtt/test"}):
     return requests.post(url=config.BASE_URL + "/api/v2/subscribe", headers={"Authorization": config.default_jwt}, json={"app": app, "driver": driver, "group": group, "params": params})
 
 
 @gen_check
-def subscribe_group_update(app, driver, group, params={}):
+def subscribe_group_update(app, driver, group, params={"topic": "/neuron/mqtt/test"}):
     return requests.put(url=config.BASE_URL + "/api/v2/subscribe", headers={"Authorization": config.default_jwt}, json={"app": app, "driver": driver, "group": group, "params": params})