忘记注册类型适配器？

尝试使用Gson转换类时，我收到有关类型适配器的错误，请帮忙。这是我的AccountBalance类，其中包含Auth Class。

import java.io.Serializable;

import com.google.gson.Gson;
import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

    public class AccountBalance implements Serializable
    {

        @SerializedName("authorization_credentials")
        @Expose
        private Authorization_credentials authorization_credentials;
        @SerializedName("corporate_no")
        @Expose
        private String corporate_no;
        @SerializedName("msisdn")
        @Expose
        private String msisdn;
        @SerializedName("account_number")
        @Expose
        private String account_number;
        private final static long serialVersionUID = 7694553150839905572L;

        public Authorization_credentials getAuthorization_credentials() {
            return authorization_credentials;
        }

        public void setAuthorization_credentials(Authorization_credentials authorization_credentials) {
            this.authorization_credentials = authorization_credentials;
        }

        public AccountBalance withAuthorization_credentials(Authorization_credentials authorization_credentials) {
            this.authorization_credentials = authorization_credentials;
            return this;
        }

        public String getCorporate_no() {
            return corporate_no;
        }

        public void setCorporate_no(String corporate_no) {
            this.corporate_no = corporate_no;
        }

        public AccountBalance withCorporate_no(String corporate_no) {
            this.corporate_no = corporate_no;
            return this;
        }

        public String getMsisdn() {
            return msisdn;
        }

        public void setMsisdn(String msisdn) {
            this.msisdn = msisdn;
        }

        public AccountBalance withMsisdn(String msisdn) {
            this.msisdn = msisdn;
            return this;
        }

        public String getAccount_number() {
            return account_number;
        }

        public void setAccount_number(String account_number) {
            this.account_number = account_number;
        }

        public AccountBalance withAccount_number(String account_number) {
            this.account_number = account_number;
            return this;
        }

        @Override
        public String toString() {
            Gson gson = new Gson();
            String json = gson.toJson(Authorization_credentials.class);
            return  json;
        }
    }

这是我需要的其他班级..谢谢

import java.io.Serializable;

import com.google.gson.Gson;
import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;


public class Authorization_credentials implements Serializable
{

    @SerializedName("api_key")
    @Expose
    private String api_key;
    @SerializedName("token")
    @Expose
    private String token;
    private final static long serialVersionUID = 8239940692560349228L;

    public String getApi_key() {
        return api_key;
    }

    public void setApi_key(String api_key) {
        this.api_key = api_key;
    }

    public Authorization_credentials withApi_key(String api_key) {
        this.api_key = api_key;
        return this;
    }

    public String getToken() {
        return token;
    }

    public void setToken(String token) {
        this.token = token;
    }

    public Authorization_credentials withToken(String token) {
        this.token = token;
        return this;
    }

    @Override
    public String toString() {
        Gson gson = new Gson();
        String json = gson.toJson(Authorization_credentials.class);
        return  json;
    }
}