Why does `esp_bt_gap_register_callback` reject NULL callback?

[vyo2003]

I'm currently digging into Bluetooth stack of ESP32 and have stumped upon one weird thing: esp_bt_gap_register_callback specifically rejects NULL callback, in turn making it impossible to disable callback completely. Here's esp_bt_gap_register_callback:

Code: [Select all] [Expand/Collapse]

1. esp_err_t esp_bt_gap_register_callback(esp_bt_gap_cb_t callback)
2. {
3.     if (esp_bluedroid_get_status() != ESP_BLUEDROID_STATUS_ENABLED) {
4.         return ESP_ERR_INVALID_STATE;
5.     }
6.  
7.     if (callback == NULL) {
8.         return ESP_FAIL;
9.     }
10.  
11.     btc_profile_cb_set(BTC_PID_GAP_BT, callback);
12.     return ESP_OK;
13. }

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The only place callback is retrieved is here:

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1. static inline void btc_gap_bt_cb_to_app(esp_bt_gap_cb_event_t event, esp_bt_gap_cb_param_t *param)
2. {
3.     esp_bt_gap_cb_t cb = (esp_bt_gap_cb_t)btc_profile_cb_get(BTC_PID_GAP_BT);
4.     if (cb) {
5.         cb(event, param);
6.     }
7. }

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(Note: inline does not do a thing here) As you can see, there's an explicit check for presence of callback. Moreover, callback is NULL by default and it's possible to manually reset it using btc_profile_cb_set directly!

So what's the reason behind banning such reset using simply esp_bt_gap_register_callback?