input: Write a python function to sort a list of dictionaries by salary in descending order.
  assert sort_employees_by_salary([{'name': 'John Doe', 'salary': 60000}, {'name': 'Jane Doe', 'salary': 50000}, {'name': 'Mary Doe', 'salary': 70000}]) == [{'name': 'Mary Doe', 'salary': 70000}, {'name': 'John Doe', 'salary': 60000}, {'name': 'Jane Doe', 'salary': 50000}]
  assert sort_employees_by_salary([{'name': 'Alice', 'salary': 30000}, {'name': 'Bob', 'salary': 100000}, {'name': 'Charlie', 'salary': 50000}]) == [{'name': 'Bob', 'salary': 100000}, {'name': 'Charlie', 'salary': 50000}, {'name': 'Alice', 'salary': 30000}]
  assert sort_employees_by_salary([]) == []
output: def sort_employees_by_salary(employees):
      return sorted(employees, key=lambda x: x['salary'], reverse=True)