Advance this and retrieve the next member in the object.
If the end of the object is reached, false is returned and
are set to invalid values. After that point, the this is invalid.
The order in which members are returned by the iterator is undefined. The iterator is invalidated if its Object is modified during iteration.
See also: next_ordered
return location for the member name, or null to ignore
return location for the member value, or null to ignore