chore: fix db connector nil pointer dereference

server/service/system/sys_user.go

@@ -2,6 +2,7 @@ package system
 
 import (
 	"errors"
+	"fmt"
 
 	"github.com/flipped-aurora/gin-vue-admin/server/global"
 	"github.com/flipped-aurora/gin-vue-admin/server/model/common/request"
@@ -39,6 +40,10 @@ func (userService *UserService) Register(u system.SysUser) (err error, userInter
 //@return: err error, userInter *model.SysUser
 
 func (userService *UserService) Login(u *system.SysUser) (err error, userInter *system.SysUser) {
+	if nil == global.GVA_DB {
+		return fmt.Errorf("db not init"), nil
+	}
+
 	var user system.SysUser
 	u.Password = utils.MD5V([]byte(u.Password))
 	err = global.GVA_DB.Where("username = ? AND password = ?", u.Username, u.Password).Preload("Authorities").Preload("Authority").First(&user).Error