You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: input_yaml.go
    path of file: ./repos/trdsql
    
    the code of the file until where you have to start completion: package trdsql

import (
	"bytes"
	"errors"
	"fmt"
	"io"
	"log"
	"strings"

	"github.com/goccy/go-yaml"
	"github.com/itchyny/gojq"
)

// YAMLReader provides methods of the Reader interface.
type YAMLReader struct {
	reader    *yaml.Decoder
	query     *gojq.Query
	already   map[string]bool
	inNULL    string

    
func (r *YAMLReader) toString(val any) any {
	var str string
	switch t := val.(type) {
	case nil:
		return nil
	case map[string]any, []yaml.MapSlice, []any:
		b, err := yaml.Marshal(val)
		if err != nil {
			log.Printf("ERROR: YAMLString:%s", err)
		}
		str = yamlToStr(b)
	case []byte:
		str = yamlToStr(t)
	case string:
		str = yamlToStr([]byte(t))
	default:
		str = ValString(t)
	}
	// Remove the last newline.
	str = strings.TrimRight(str, "\n")
	if r.needNULL {
		return replaceNULL(r.inNULL, str)
	}
	return str
}