Determine whether the return operation was successful or not

Hi everyone,

I have an assignment, but I don't fully understand what is asked here. I would be glad if you help. 

         //handicap ;
         // It's made to work only on the Person object. Salary will need to duplicate the code to do the same.
         // It is decided whether there is an error in the return, whether the string content is full or not.

         //Expectation :

         //This code is operable for any desired object (all objects).
         //Determine whether the return operation was successful or not, and only if the return was unsuccessful, then the content is displayed.

         // This is how you edit the code. (Type : Reflection, Attributes, CustomAttributes,)

        static void Main(string[] args)
        {
            Person person = new Person();

            var result = person.PropertyNullorEmptyCheck();

            if (result != "") Console.WriteLine(result);



            //Salary salary = new Salary();

            //result = salary.PropertyNullorEmptyCheck();

            //if (result != "") Console.WriteLine(result);
        }
 

        public class Person
        {

            [Required]

            public string Id { get; set; }

            [Required]

            public string Name { get; set; }

            [Required]

            public string Surname { get; set; }

            [Required]

            public string Email { get; set; }

            [Required]

            public string Phone { get; set; }

            [Required]
            public string Address { get; set; }
          
        }



        public class Salary

        {

            [Required]

            public string Id { get; set; }

            [Required]

            public double Pay { get; set; }

        }



        public static partial class GlobalProcess
        {

            public static string PropertyNullorEmptyCheck(this Person person)

            {

                string list = "";



                list = list + (string.IsNullOrEmpty(person.Id) ? "Id bos olamaz. \n" : "");

                list = list + (string.IsNullOrEmpty(person.Name) ? "Name bos olamaz. \n" : "");

                list = list + (string.IsNullOrEmpty(person.Surname) ? "Surname bos olamaz. \n" : "");

                list = list + (string.IsNullOrEmpty(person.Email) ? "Email bos olamaz. \n" : "");

                list = list + (string.IsNullOrEmpty(person.Phone) ? "Phone bos olamaz. \n" : "");

                list = list + (string.IsNullOrEmpty(person.Address) ? "Address bos olamaz. \n" : "");



                return list;

            }

        }