As far as I am aware, a proper 'null consonant' has only arisen when it
actually represents a glottal stop.
There's ㅇ in hangeul ("Hangul"; Korean). Hebrew ע was supposedly first
pharyngeal [ʕ], though it's nowadays standardly a glottal stop [ʔ] or
null ∅ (and you don't even need need a hiatus for this). It's not clear
to me to what extent it's correct to say that Arabic alif arose from a
glottal stop (given that it was effectively used for [a:] too).
(Thx for the info on Thai and Khmer.)
It's occurring to me that the modern analogue to the quirky grammarian
completing the table for the sake of symmetry would be the guy on the
Unicode mailing list wanting to add characters to the Standard merely to
complete a partial list :-)
Stephan
