Table: `Employee`

    +-------------+------+
    | Column Name | Type |
    +-------------+------+
    | id          | int  |
    | salary      | int  |
    +-------------+------+
    id is the primary key column for this table.
    Each row of this table contains information about the salary of an employee.

Write an SQL query to report the `nth` highest salary from the `Employee` table. If there is no `nth` highest salary, the query should report `null`.

The query result format is in the following example.

Example 1:

    Input:
    Employee table:
    +----+--------+
    | id | salary |
    +----+--------+
    | 1  | 100    |
    | 2  | 200    |
    | 3  | 300    |
    +----+--------+
    n = 2
    Output:
    +------------------------+
    | getNthHighestSalary(2) |
    +------------------------+
    | 200                    |
    +------------------------+

Example 2:

    Input:
    Employee table:
    +----+--------+
    | id | salary |
    +----+--------+
    | 1  | 100    |
    +----+--------+
    n = 2
    Output:
    +------------------------+
    | getNthHighestSalary(2) |
    +------------------------+
    | null                   |
    +------------------------+