Previously, if a field nested beneath an optional field was documented
and was required, it would be identified as missing even if its
optional ancestor was missing. This made it impossible to document
required fields of an optional subsection of a payload.
This commit updates JsonContentHandler to consider a field’s ancestors
when determining if it should be reported as missing. If the field
field has an optional ancestor that is not present, the field is not
considered to be missing if it too is not present. If the field has
an optional ancestor that is present then the field is considered to
be missing if it is not present.
Closes gh-429