presto-main/src/main/java/io/prestosql/sql/planner/EqualityInference.java/EqualityInference/getCanonical
class EqualityInference:    private static Expression getCanonical(Collection<Expression> expressions)
    {
        if (expressions.isEmpty()) {
            return null;
        }
        return CANONICAL_ORDERING.min(expressions);
    }