multirange constructor strictness

The multirange constructors created in makeMultirangeConstructors() are:

multirange_constructor0 -> not strict
multirange_constructor1 -> strict
multirange_constructor2 -> not strict

And both multirange_constructor1 and multirange_constructor2 contain
code like

/*
* These checks should be guaranteed by our signature, but let's do them
* just in case.
*/
if (PG_ARGISNULL(0))
ereport(ERROR,
(errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
errmsg("multirange values cannot contain NULL members")));

In case of multirange_constructor2 the "should be guaranteed" comment is
not actually true right now. In case of multirange_constructor1, maybe
this should be downgraded to an elog or assert or just removed.

Is there a reason why we can't make them all three strict or all not
strict? (Obviously, it doesn't matter for multirange_constructor0.) Is
the fact that multirange_constructor2 is variadic the issue? Maybe at
least some more comments would be helpful.