asp.net - Blank Json modelState key from UserManager PasswordValidator -

using usermanager set password validation:

usermanager.passwordvalidator = new passwordvalidator         {             requiredlength = 6,             requirenonletterordigit = true,             requiredigit = false,             requirelowercase = true,             requireuppercase = true,         }; 

when make call change password via api, response if password not valid is:

{   "message": "the request invalid.",   "modelstate": {     "": [       "passwords must have @ least 1 non letter or digit character. passwords must have @ least 1 uppercase ('a'-'z')."     ]   } } 

how set blank modelstate key property?