The BOARD variable is not defined at the top of CmakeLists.txt on ncs2.8.0

[loquat]

I work test program on ncs2.8.0.

I put a reference to the BOARD variable at the top of my project's CMakeLists.txt.

When "west build -b nrf52833dk_nrf52833",  BOARD is not defined.

But,

When "cmake -GNinja -DBOARD=nrf52833dk_nrf52833 ..",  BOARD is nrf52833dk_nrf52833.

This was not a problem in ncs2.6.0.
Please tell me how to reference the BOARD in ncs2.8.0.