Minor Description
facet.limit constraints the number of term values returned for a field when using facet.field or facet.pivot, but that limit is (suppose) to be independent of facet.missing, which adds an additional count beyond the facet.limit for docs that are "missing" that field.
This works fine for facet.limit >= 1, but if you use facet.limit=0&facet.missing=true (ie: you are only interested in the missing count) you get no counts at all – not even for the missing count.