if语法的错误

该方法编译报错，但不知报错的原因啊，先做个记录

public static int a(Map<String, Object> parameters){
		
		Map<String, Object> username = new HashMap<String, Object>();
		username.put("username", parameters.get("username"));
		
		if(null != parameters.get("username"))
			String a = "";
		
		
			return 0;
	}