bson_iter_next man page
bson_iter_next — bson_iter_next()
bool bson_iter_next (bson_iter_t *iter);
iter: A bson_iter_t.
Advances iter to the next element in the document.
true if iter was advanced. Returns false if iter has passed the last element in the document or encountered invalid BSON.
It is a programming error to use iter after this function has returned false.
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