FLUTTER => password and confirm password field validation before the creation of a user. Handles all edge cases well without blocking user input at any point.

main.dart

  String getPasswordValidationError(bool forPassword) {
    String initialPasswordString = focusNodeToValue[passwordFocusNode].value;
    String confirmPasswordString = focusNodeToValue[confirmPasswordFocusNode].value;

    ///-----make sure this particular password is valid
    if (forPassword) {
      if (initialPasswordString.isNotEmpty == false)
        return "Password Required";
      else if (initialPasswordString.length < 6)
        return "The Password Requires 6 Characters Or More";
    } else {
      if (confirmPasswordString.isNotEmpty == false)
        return "Password Required";
      else if (confirmPasswordString.length < 6)
        return "The Password Requires 6 Characters Or More";
    }

    //Note: we don't check our counter part here because we assume that either
    //1. It has yet to be filled out
    //    - so we don't scare our user with red
    //2. It has been filled out...
    //  2a. and it has its own individual error
    //    - where its implicit the passwords don't match because it didn't even pass its individual tests
    //    - much less match up to us that did pass our individual tests [because otherwise we would have returned by now]
    //    - consequently, showing individual error reveals more than just saying that the passwords don't match
    //  2b. and it does not have it own individual error
    //    - so now it must be checked against us

    ///-----make sure both passwords are valid together
    if (initialPasswordString.isNotEmpty && confirmPasswordString.isNotEmpty) {
      if (initialPasswordString != confirmPasswordString){
        //this particular case means that we are valid... but it only says that our counter part is not empty
        //so this revels 2 cases for our counter part
        //  1. It doesn't meet all of its individual tests
        //    - in which case as explained above, the individual error should stay because its more descriptive
        //  2. It does meet all of its individual tests
        //    - in which case it might be best to also indicate in its field that the passwords don't match
        if(forPassword && focusNodeToError[confirmPasswordFocusNode].value == null){
          focusNodeToError[confirmPasswordFocusNode].value = "The Passwords Don't Match";
        }
        else if(focusNodeToError[passwordFocusNode].value == null){
          focusNodeToError[passwordFocusNode].value = "The Passwords Don't Match";
        }

        return "The Passwords Don't Match";
      }
      else {
        //this particular case means that we are valid... and our counter part is valid... and it matches us
        //however although our error will be cleared out, our counter part might have had an error and it has to be cleared out too
        if(forPassword) focusNodeToError[confirmPasswordFocusNode].value = null;
        else focusNodeToError[passwordFocusNode].value = null;

        return null;
      }
    } else {
      //this particular case means that we are valid... but our counter part is empty
      //our counter part can be empty for 2 reasons
      //  1. it was never filled out
      //    - in which case we don't want to scare our users with red
      //  2. it was filled out and erased
      //    - in which case the individual error will already be shown
      return null;
    }
  }

  String getInitialPasswordValidationError() => getPasswordValidationError(true);
  String getConfirmPasswordValidationError() => getPasswordValidationError(false);

Error Occured : Undefined name focusNodeToError
How can i solve this error?