问颤振json_serializable构建失败

EN

Account(String id, String firstName, String lastName, String email,
  DateTime dob, DateTime created, DateTime updated,
  {String accessTkn, String refreshTkn}) {}

import "package:json_annotation/json_annotation.dart";

part "account.g.dart";

@JsonSerializable(nullable: true)
class Account {
  @JsonKey(name: "id")
  String _id;

  @JsonKey(name: "first_name")
  String _firstName;

  @JsonKey(name: "last_name")
  String _lastName;

  @JsonKey(name: "email")
  String _email;

  @JsonKey(
      name: "dob", fromJson: _isoStringToDateTime, toJson: _dateTimeToIsoString)
  DateTime _dob;

  @JsonKey(
      name: "created",
      fromJson: _isoStringToDateTime,
      toJson: _dateTimeToIsoString)
  DateTime _created;

  @JsonKey(
      name: "updated",
      fromJson: _isoStringToDateTime,
      toJson: _dateTimeToIsoString)
  DateTime _updated;

  @JsonKey(name: "access_token")
  String _accessToken;

  @JsonKey(name: "refresh_token")
  String _refreshToken;

  Account(String id, String firstName, String lastName, String email,
      DateTime dob, DateTime created, DateTime updated,
      {String accessTkn, String refreshTkn}) {
    this._id = id;
    this._firstName = firstName;
    this._lastName = lastName;
    this._email = email;
    this._dob = dob;
    this._created = created;
    this._updated = updated;
    this._accessToken = accessToken;
    this._refreshToken = refreshTkn;
  }

  factory Account.fromJson(Map<String, dynamic> json) {
    _$AccountFromJson(json);
  }

  // converts a DateTime to a ISO string
  static String _dateTimeToIsoString(DateTime date) {
    return date.toIso8601String();
  }

  // convert back to date time
  static DateTime _isoStringToDateTime(String iso) {
    return DateTime.parse(iso);
  }

  /// get the account id
  String get id {
    return this._id;
  }

  /// get the account first name
  String get firstName {
    return this._firstName;
  }

  /// get the account last name
  String get lastName {
    return this._lastName;
  }

  /// get the account email.
  String get email {
    return this._email;
  }

  /// get the account owner's date of birth
  DateTime get dob {
   return this._dob;
  }

  /// Get the date the account was created.
  DateTime get createdAt {
    return this._created;
  }

  /// get teh date the account was last updated.
  DateTime get updatedAt {
   return this._updated;
  }

  // get the account access token.
  String get accessToken {
    return this._accessToken;
  }

  // get the account refresh token.
  String get refreshToken {
    return this._refreshToken;
  }

  /// clones the account instance
  Account clone() {
    return Account(this.id, this.firstName, this.lastName, this.email, this.dob,
        this.createdAt, this.updatedAt,
        accessTkn: this.accessToken, refreshTkn: this.refreshToken);
  }

  Map<String, dynamic> toJson() {
    _$AccountToJson(this);
  }
}