连接SQL Server总是报空指针异常。。。下面是configPlugins里的代码

    // sqlserver
        String url = getProperty("jdbc.url").trim();
        String username = getProperty("jdbc.username").trim();
        String password = getProperty("jdbc.password").trim();
        String driverClass = getProperty("jdbc.driverClassName").trim();
        
        // 配置C3p0数据库连接池插件
        C3p0Plugin c3p0Plugin = new C3p0Plugin(url, username, password, driverClass);
        me.add(c3p0Plugin);
          
        // 配置ActiveRecord插件
        ActiveRecordPlugin arp = new ActiveRecordPlugin(c3p0Plugin);
        arp.setDialect(new SqlServerDialect());
        me.add(arp);

严重: Exception starting filter JFinalFilter
java.lang.NullPointerException
    at com.jfinal.plugin.activerecord.Model.find(Model.java:567)
    at com.jfinal.plugin.activerecord.Model.findFirst(Model.java:594)
    at com.jfinal.plugin.activerecord.Model.findFirst(Model.java:603)
    at com.jfinalshop.model.Orders.getLastOrderSn(Orders.java:119)
    at com.jfinalshop.util.SerialNumberUtil.lastSnNumberInit(SerialNumberUtil.java:52)
    at com.jfinalshop.cfg.JFWebConfig.afterJFinalStart(JFWebConfig.java:138)
    at com.jfinal.core.JFinalFilter.init(JFinalFilter.java:55)
    at org.apache.catalina.core.ApplicationFilterConfig.initFilter(ApplicationFilterConfig.java:279)
    at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:260)
    at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:105)
    at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4855)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5549)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1574)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1564)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)