input: Write a function to create a dictionary containing student names as keys and their corresponding marks as values. If no input is provided, return an empty dictionary.
  assert construct_student_marks_dict({"John" : 90, "Levi" : 85, "Jill" : 95, "Sara" : 75})=={"John" : 90, "Levi" : 85, "Jill" : 95, "Sara" : 75}
  assert construct_student_marks_dict({})=={}
output: def construct_student_marks_dict(student_marks=None):
      if student_marks is None:
          return {}
      return student_marks