source is null for getProperty(null, "2")

[nizhuancaipan]

• 我已经在 issues 里搜索，没有重复的issue。

环境信息

• arthas-boot.jar 或者 as.sh 的版本： 4.1.2

-12-17 16:06:30 [syncDataThreadPool5-1] WARN  c.t.a.c.c.m.TimeTunnelAdviceListener -tt failed.
com.taobao.arthas.core.command.express.ExpressException: ognl.OgnlException: source is null for getProperty(null, "2")
	at com.taobao.arthas.core.command.express.OgnlExpress.get(OgnlExpress.java:39)
	at com.taobao.arthas.core.command.express.OgnlExpress.is(OgnlExpress.java:45)
	at com.taobao.arthas.core.advisor.AdviceListenerAdapter.isConditionMet(AdviceListenerAdapter.java:119)
	at com.taobao.arthas.core.command.monitor200.TimeTunnelAdviceListener.afterFinishing(TimeTunnelAdviceListener.java:75)
	at com.taobao.arthas.core.command.monitor200.TimeTunnelAdviceListener.afterReturning(TimeTunnelAdviceListener.java:58)
	at com.taobao.arthas.core.advisor.AdviceListenerAdapter.afterReturning(AdviceListenerAdapter.java:57)
	at com.taobao.arthas.core.advisor.SpyImpl.atExit(SpyImpl.java:68)
	at java.arthas.SpyAPI.atExit(SpyAPI.java:64)

这个一般是什么原因导致的。