How can I throw an error if a parameter is null or 0?

I have this stored procedure:

CREATE PROCEDURE [dbo].[get_test_status]
    @CreatedBy      INT OUTPUT,
    @TestStatusId   INT OUTPUT,
    @UserTestId     INT,
    @UserId         INT
AS

How can I throw an error if the @UserId parameter is a null or zero ?

Here's what I tried but it gives a syntax error:

IF (@UserId = 0 OR @UserId IS NULL)
    THROW 70001, "UserId: Cannot be zero or null" , 1