  This paper describes the electrodynamics of a null and force-free field in
completely geometric terms. As was previously established in \cite{Menon_FF20},
solutions to force-free electrodynamics are governed by the existence of
certain special types of foliations of spacetime. Here the nature of the
foliations in a coordinate-free formalism in the null case is prescribed. All
of the general results are illustrated by constructing a null, force-free
electrodynamic field in a Friedmann-Lemaitre-Robertson- Walker (FLRW)
spacetime.
