presto-spi/src/main/java/io/prestosql/spi/type/VarcharType.java/VarcharType/VarcharType
class VarcharType:    private VarcharType(int length)
    {
        super(
                new TypeSignature(
                        StandardTypes.VARCHAR,
                        singletonList(TypeSignatureParameter.numericParameter((long) length))),
                Slice.class);

        if (length < 0) {
            throw new IllegalArgumentException("Invalid VARCHAR length " + length);
        }
        this.length = length;
    }