Notify on succeeds while no apparent descriptor

I have a bogus BLE device which exposes "badly" a characteristic
notification. Even though it doesn't find a characteristic descriptor,
I'm still able to start notifications and even receive value changed
events.

For info, Android and macOS raise an exception when trying to start
notifications. See
https://github.com/WebBluetoothCG/ble-test-peripheral-android/issues/63

See logs:

< ACL Data TX: Handle 32 flags 0x00 dlen 9
                                                   [hci0] 403.621325
      ATT: Find Information Request (0x04) len 4
        Handle range: 0x002b-0xffff

HCI Event: Number of Completed Packets (0x13) plen 5                                                                    [hci0] 403.689256

        Num handles: 1
        Handle: 32
        Count: 1

ACL Data RX: Handle 32 flags 0x02 dlen 9                                                                                [hci0] 403.755926

      ATT: Error Response (0x01) len 4
        Find Information Request (0x04)
        Handle: 0x002b
        Error: Attribute Not Found (0x0a)

---

[Nexus 5X]# list-attributes
Primary Service
        /org/bluez/hci0/dev_46_EE_57_93_31_08/service0001
        Generic Attribute Profile
Characteristic
        /org/bluez/hci0/dev_46_EE_57_93_31_08/service0001/char0002
        Service Changed
Primary Service
        /org/bluez/hci0/dev_46_EE_57_93_31_08/service0028
        Battery Service
Characteristic
        /org/bluez/hci0/dev_46_EE_57_93_31_08/service0028/char0029
        Battery Level
[Nexus 5X]# select-attribute
/org/bluez/hci0/dev_46_EE_57_93_31_08/service0028/char0029
[Nexus 5X:/service0028/char0029]# notify on
[CHG] Attribute
/org/bluez/hci0/dev_46_EE_57_93_31_08/service0028/char0029 Notifying:
yes
Notify started
[CHG] Attribute
/org/bluez/hci0/dev_46_EE_57_93_31_08/service0028/char0029 Value: 0x32
[Nexus 5X:/service0028/char0029]# notify off
[CHG] Attribute
/org/bluez/hci0/dev_46_EE_57_93_31_08/service0028/char0029 Notifying:
no
Notify stopped