void notifyClosed() {
		if (closedCallback != null) {
			try {
				closedCallback.onClosed();
			} catch (final Throwable t) {
				Log.e(TAG, "Exception in Closed callback", t);
			}
		}
		free();
	}
Sets a callback that will be executed when the device services were invalidated (i.e. on
disconnection) or the callback has been unregistered and it can release resources.

@param callback the callback.
@return The request.
ble/src/main/java/no/nordicsemi/android/ble/ValueChangedCallback.java