public static void FilterAndTake(string courseName, string givenFilter, int?studentsToTake = null)
        {
            if (IsQueryForCoursePossible(courseName))
            {
                studentsToTake = studentsByCourse[courseName].Count;
            }

            RepositoryFilters.FilterAndTake(studentsByCourse[courseName], givenFilter, studentsToTake.Value);
        }
 // Constructor for the current class which recieves a RepositorySorter and a RepositoryFilter as parameters
 public StudentsRepository(RepositoryFilters filter, RepositorySorters sorter)
 {
     this.filter = filter;
     this.sorter = sorter;
 }