Simple Nested IF Syntax Error

[Jian Jin]

I'm creating a stored procedure on MySQL community windows version 5.7.21. The source and a syntax error are below. I'm stuck here and cannot find solutions for days, anyone can help? Thanks in advance.

[Err] 1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 7

DROP PROCEDURE IF EXISTS SP1;
CREATE PROCEDURE SP1()
BEGIN
IF (SELECT TRUE) THEN
IF (TRUE) THEN
SET @s = 1;
END IF;
END IF;
END