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