input: Write a python function to retrieve an employee's details by their employee ID from an SQLite database.
  assert get_employee(1) == {'name': 'John Doe', 'age': 30, 'designation': 'Software Engineer'}
  assert get_employee(2) == {'name': 'Jane Smith', 'age': 25, 'designation': 'Data Analyst'}
  assert get_employee(999) == None
output: def get_employee(employee_id):
      import sqlite3
  
      connection = sqlite3.connect('employees.db')
      cursor = connection.cursor()
      
      query = "SELECT name, age, designation FROM employees WHERE id = ?"
      cursor.execute(query, (employee_id,))
      result = cursor.fetchone()
      
      connection.close()
      
      if result:
          return {'name': result[0], 'age': result[1], 'designation': result[2]}
      else:
          return None