In rootfs_rpm.bbclass, INSTALL_PLATFORM_EXTRA_RPM is not exported, but it is needed by package_rpm.bbclass.
merged into poky/master: 67e056a76aac2db9cac6ddf8337bc250788f118c http://git.pokylinux.org/cgit.cgi/poky-contrib/log/?h=ChenQi/rootfs_rpm
recently tests no such error related to this change. git info: 37e025f6f9c410005e0f1dee0767e38eaec01cbd git branch: poky/master