Why does compiling module from source fails with "ERROR: modpost: missing MODULE_LICENSE()" on RHEL9?

Issue

• Why does compiling module from source fails with "ERROR: modpost: missing MODULE_LICENSE()" on RHEL9?

# make -C /lib/modules/$(uname -r)/build M=/root/testmodule modules
make: Entering directory '/usr/src/kernels/5.14.0-1.3.1.el9.x86_64'
CC [M] /root/testmodule/test.o
MODPOST /root/testmodule/Module.symvers
ERROR: modpost: missing MODULE_LICENSE() in /root/testmodule/test.o
make[1]: * [scripts/Makefile.modpost:150: /root/testmodule/Module.symvers] Error 1
make[1]: * Deleting file '/root/testmodule/Module.symvers'
make: * [Makefile:1776: modules] Error 2
make: Leaving directory '/usr/src/kernels/5.14.0-1.3.1.el9.x86_64'