presto-main/src/main/java/io/prestosql/operator/scalar/StringFunctions.java/StringFunctions/fromUtf8
class StringFunctions:    @Description("decodes the UTF-8 encoded string")
    @ScalarFunction
    @SqlType(StandardTypes.VARCHAR)
    public static Slice fromUtf8(@SqlType(StandardTypes.VARBINARY) Slice slice, @SqlType(StandardTypes.BIGINT) long replacementCodePoint)
    {
        if (replacementCodePoint > MAX_CODE_POINT || Character.getType((int) replacementCodePoint) == SURROGATE) {
            throw new PrestoException(INVALID_FUNCTION_ARGUMENT, "Invalid replacement character");
        }
        return SliceUtf8.fixInvalidUtf8(slice, OptionalInt.of((int) replacementCodePoint));
    }