Undefined symbol advertising_stop (referred from main.o)

Question

I have this error but dont know why. Because I have a function which is called advertising_stop(). I would like to implement the DFU part in my function but this error doesnt want to disappear. 
 Im using a nRF51422 and Keil v5 
 ifdef BLE_DFU_APP_SUPPORT 
 static void advertising_stop(void)
{ 
 uint32_t err_code;
err_code = sd_ble_gap_adv_stop();
APP_ERROR_CHECK(err_code);

nrf_gpio_pin_clear(ADVERTISING_LED_PIN_NO);
 
 }
... 
 ... 
 static void reset_prepare(void)
{
uint32_t err_code; 
 if (m_conn_handle != BLE_CONN_HANDLE_INVALID)
{
 // Disconnect from peer.
 err_code = sd_ble_gap_disconnect(m_conn_handle, BLE_HCI_REMOTE_USER_TERMINATED_CONNECTION);
 APP_ERROR_CHECK(err_code);
}
else
{
 // If not connected, then the device will be advertising. Hence stop the advertising.
 advertising_stop();
}

nrf_gpio_pin_clear(ADVERTISING_LED_PIN_NO);
nrf_gpio_pin_clear(CONNECTED_LED_PIN_NO);

err_code = ble_conn_params_stop();
APP_ERROR_CHECK(err_code);
 
 }

Inspectron · Accepted Answer

Problem is fixed. Commands inside the condition group will not be compiled or be referred to if the macro BLE_DFU_APP_SUPPORT is not defined. 
 You can define BLE_DFU_APP_SUPPORT in C/C++ tab in the Project option. You can either remove the conditional group instructions or you can define the BLE_DFU_APP_SUPPORT in your code or in C/C++ tab.