We recommend reading this documentation on pkgdown which renders math nicely.
https://pkg.mitchelloharawild.com/distributional/reference/dist_missing.html
The missing distribution represents the absence of distributional
information. It is used as a placeholder when distribution values are
not available or not applicable, similar to how NA is used for missing
scalar values.
Support: Undefined
Mean: \(\text{NA}\)
Variance: \(\text{NA}\)
Skewness: \(\text{NA}\)
Kurtosis: \(\text{NA}\)
Probability density function (p.d.f): Undefined
$$
f(x) = \text{NA}
$$
Cumulative distribution function (c.d.f): Undefined
$$
F(t) = \text{NA}
$$
Quantile function: Undefined
$$
Q(p) = \text{NA}
$$
Moment generating function (m.g.f): Undefined
$$
E(e^{tX}) = \text{NA}
$$
All statistical operations on missing distributions return NA values
of appropriate length, propagating the missingness through calculations.