query method
Search for intervals in the index which intersect the given closed interval and apply the visitor to them.
@param min the lower bound of the query interval @param max the upper bound of the query interval @param visitor the visitor to pass any matched items to
Implementation
void query(double min, double max, ItemVisitor visitor) {
init();
// if root is null tree must be empty
if (root == null) return;
root!.query(min, max, visitor);
}