@NonNull
	protected ValueChangedCallback setIndicationCallback(@Nullable final BluetoothGattCharacteristic characteristic) {
		return setNotificationCallback(characteristic);
	}
Returns the callback that is registered for value changes (indications) of given
characteristic. After assigning the indication callback, indications must be
enabled using {@link #enableIndications(BluetoothGattCharacteristic)}.
This applies also when they were already enabled on the remote side.
<p>
To remove the callback, call
{@link #removeIndicationCallback(BluetoothGattCharacteristic)}.

@param characteristic characteristic to bind the callback with. If null, the returned
                      callback will not be null, but will not be used.
@return The callback.
ble/src/main/java/no/nordicsemi/android/ble/BleManager.java