Zephyr example-application failed to build

[DaGigabyte]

When building the example-application from https://github.com/zephyrproject-rtos/example-application
using west build -b custom_plank in the example-application root directory, I encountered the following error:

my-app/app/prj.conf:7: warning: attempt to assign the value 'y' to the undefined symbol BLINK

error: Aborting due to Kconfig warnings

Is the example-application compilable using that command above?