@uml
Return a new {@link IntSet} object containing all elements that are
present in both the current set and the specified set {@code a}.
@param a The set to intersect with the current set. A {@code null}
argument is treated as though it were an empty set.
@return A new {@link IntSet} instance containing the intersection of the
current set and {@code a}. The value {@code null} may be returned in
place of an empty result set.
@uml Return a new {@link IntSet} object containing all elements that are present in both the current set and the specified set {@code a}.
@param a The set to intersect with the current set. A {@code null} argument is treated as though it were an empty set. @return A new {@link IntSet} instance containing the intersection of the current set and {@code a}. The value {@code null} may be returned in place of an empty result set.