开发笔记:尝试从Firebase数据库获取时无法获取CarType

当我清除我的应用程序缓存时，当我尝试运行应用程序时，我收到以下错误它工作正常但是当我关闭它并再次运行它崩溃

Attempt to invoke virtual method 'java.lang.String com.ggsbusiness.amirmemon.comsatsbusservice.Model.ComsatsDriver.getCarType()' on a null object reference


当试图从Firebasedatabse获取当前的cartype时。

drivers = FirebaseDatabase.getInstance().getReference(Common.driver_tbl).child(Common.currentBusDriver.getCarType());


来自Common.class

public class Common {
public static final String driver_tbl = "Drivers";
public static final String user_driver_tbl = "DriversInformation";
public static final String user_rider_tbl = "RidersInformation";
public static final String pickup_request_tbl = "PickupRequest";
public static final String baseURL = "https://maps.googleapis.com";
public static ComsatsDriver currentBusDriver;
public static IGoogleAPI getGoogleAPI()
{
return RetrofitClient.getClient(baseURL).create(IGoogleAPI.class);
}
}


这是ComsatsDriver.class：

public class ComsatsDriver {
private String name,phone,carType;
public ComsatsDriver(){
}
public ComsatsDriver(String name, String phone, String carType) {
this.name = name;
this.phOne= phone;
this.carType = carType;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPhone() {
return phone;
}
public void setPhone(String phone) {
this.phOne= phone;
}
public String getCarType() {
return carType;
}
public void setCarType(String carType) {
this.carType = carType;
}
}