-static xbt_dict_t comm_lookup = NULL;
-static xbt_dict_t group_lookup = NULL;
-static xbt_dict_t request_lookup = NULL;
-static xbt_dict_t datatype_lookup = NULL;
-static xbt_dict_t op_lookup = NULL;
-static xbt_dict_t win_lookup = NULL;
-static xbt_dict_t info_lookup = NULL;
+static xbt_dict_t comm_lookup = nullptr;
+static xbt_dict_t group_lookup = nullptr;
+static xbt_dict_t request_lookup = nullptr;
+static xbt_dict_t datatype_lookup = nullptr;
+static xbt_dict_t op_lookup = nullptr;
+static xbt_dict_t win_lookup = nullptr;
+static xbt_dict_t info_lookup = nullptr;