Arduino-ESP32 - Solution to "Invalid library found"

After updating Arduino-ESP32, I notice that there is a line of message at the bottom of the message window of Arduino IDE.

The message reads "Invalid library found in C:\Users\WeiHsiungHuang\Documents\Arduino\hardware\espressif\esp32\libraries\BLE: C:\Users\WeiHsiungHuang\Documents\Arduino\hardware\espressif\esp32\libraries\BLE"

The solution

1. Launch Command Prompt Window;

2. Change working directory to "Arduino\hardware\espressif\esp32";

3. Issue the command "git submodule update --init --recursive";

4. Re-compile the Arduino sketch and check the message in the message window.

Reference:

Invalid library BLE
https://github.com/espressif/arduino-esp32/issues/766