Blank help texts are probably either a typo, a Kconfig misunderstanding,
or some kind of half-committing to adding a help text (in which case a
TODO comment would be clearer, if the help text really can't be added
right away).
Best to flag them, IMO.
Example warning:
drivers/mmc/host/Kconfig:877: warning: 'MMC_TOSHIBA_PCI' defined with blank help text