failed to initialize database, got error dial tcp :0: connectex: The requested address is not valid in its context.
panic: DB Error: dial tcp :0: connectex: The requested address is not valid in its context.
goroutine 1 [running]:
ToDoList-Server/model.DBConnection()
        C:/Users/81804/enviroment/todo/ToDoList-Server/model/db.go:21 +0x225
main.main()
        C:/Users/81804/enviroment/todo/ToDoList-Server/main.go:10 +0x2a

package model
import (
	"database/sql"
	"fmt"
	"os"
	_ "github.com/go-sql-driver/mysql"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
)
var db *gorm.DB
// DB接続とテーブルを作成する
func DBConnection() *sql.DB {
	dsn := GetDBConfig()
    var err error
	db, err = gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(fmt.Errorf("DB Error: %w", err))
	}
	CreateTable(db)
	sqlDB, err := db.DB()
	if err != nil {
		panic(fmt.Errorf("DB Error: %w", err))
	}
	return sqlDB
}
// DBのdsnを取得する
func GetDBConfig() string {
	user := os.Getenv("DB_USERNAME")
	password := os.Getenv("DB_PASSWORD")
	hostname := os.Getenv("DB_HOSTNAME")
	port := os.Getenv("DB_PORT")
	dbname := os.Getenv("DB_DBNAME")
	dsn := fmt.Sprintf("%s:%s@tcp(%s:%s)/%s", user, password, hostname, port, dbname) + "?charset=utf8mb4&parseTime=True&loc=Local"
	return dsn
}
// Task型のテーブルを作成する
func CreateTable(db *gorm.DB) {
	db.AutoMigrate(&Task{})
}

dsn := fmt.Sprintf("host=%s user=%s password=%s dbname=%s post=%s", hostname, user, password, dbname, port)