presto-main/src/main/java/io/prestosql/type/TypeCoercion.java/TypeCoercion/isCovariantParametrizedType
class TypeCoercion:    private static boolean isCovariantParametrizedType(Type type)
    {
        // if we ever introduce contravariant, this function should be changed to return an enumeration: INVARIANT, COVARIANT, CONTRAVARIANT
        return type instanceof MapType || type instanceof ArrayType;
    }