UART0_IRQHandler doesn't called in UART sample

Question

I am running 5.2 sdk's UART under experimenta\ble_app_uart,
I assume it works with www.nordicsemi.com/.../nRF-UART-2.0-for-Android-4.3 
 when Android app sends data to device, it is able to received in
void nus_data_handler(ble_nus_t * p_nus, uint8_t * p_data, uint16_t length)
{
for (int i = 0; i < length; i++)
{
simple_uart_put(p_data[i]);
}
simple_uart_put('
');
} 
 however, nothing was sent to APP side, no notification sent to app side too. 
 also void UART0_IRQHandler(void) did not get called 
 what did I do wrong? wrong device example code used? 
 UART0_IRQHandler seems very strange,
data_array[index] = simple_uart_get(); it return some pointer to data_array[index];
how ever, later it use index+1 as the length, and use the wrong way:(index >= (BLE_NUS_MAX_DATA_LEN - 1) 
 seems this is an example that all went wrong? 
 void UART0_IRQHandler(void)
{
static uint8_t data_array[BLE_NUS_MAX_DATA_LEN];
static uint8_t index = 0;
uint32_t err_code; 
 /**@snippet [Handling the data received over UART] */

data_array[index] = simple_uart_get();
index++;

if ((data_array[index - 1] == '
') || (index >= (BLE_NUS_MAX_DATA_LEN - 1)))
{
 err_code = ble_nus_send_string(&m_nus, data_array, index + 1);
 if (err_code != NRF_ERROR_INVALID_STATE)
 {
 APP_ERROR_CHECK(err_code);
 }
 
 index = 0;
}

/**@snippet [Handling the data received over UART] */
 
 }