Coerce a possibly-single / possibly-missing XML child into an array. A repeated element parses to an array, a single occurrence to one object, and a missing one to undefined; this normalises all three so callers always get a list.
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Coerce a possibly-single / possibly-missing XML child into an array. A repeated element parses to an array, a single occurrence to one object, and a missing one to
undefined; this normalises all three so callers always get a list.