Activiti中TaskQueryImpl时不时报错，重启服务就好了，这个是什么问题?报错

我也遇到了，怎么解决的？？？？

/*LicensedundertheApacheLicense,Version2.0(the"License");*youmaynotusethisfileexceptincompliancewiththeLicense.*YoumayobtainacopyoftheLicenseat**http://www.apache.org/licenses/LICENSE-2.0**Unlessrequiredbyapplicablelaworagreedtoinwriting,software*distributedundertheLicenseisdistributedonan"ASIS"BASIS,*WITHOUTWARRANTIESORCONDITIONSOFANYKIND,eitherexpressorimplied.*SeetheLicenseforthespecificlanguagegoverningpermissionsand*limitationsundertheLicense.*/packageorg.activiti.engine.impl.db;/***@authorDanielMeyer*/publicclassListQueryParameterObject{protectedintmaxResults=Integer.MAX_VALUE;protectedintfirstResult=0;protectedObjectparameter;protectedStringdatabaseType;publicListQueryParameterObject(){}publicListQueryParameterObject(Objectparameter,intfirstResult,intmaxResults){this.parameter=parameter;this.firstResult=firstResult;this.maxResults=maxResults;}publicintgetFirstResult(){returnfirstResult;}publicintgetFirstRow(){returnfirstResult+1;}publicintgetLastRow(){if(maxResults==Integer.MAX_VALUE){returnmaxResults;}returnfirstResult+maxResults+1;}publicintgetMaxResults(){returnmaxResults;}publicObjectgetParameter(){returnparameter;}publicvoidsetFirstResult(intfirstResult){this.firstResult=firstResult;}publicvoidsetMaxResults(intmaxResults){this.maxResults=maxResults;}publicvoidsetParameter(Objectparameter){this.parameter=parameter;}publicStringgetOrderBy(){//thedefaultordercolumnreturn"RES.ID_asc";}publicStringgetOrderByColumns(){returngetOrderBy();}publicvoidsetDatabaseType(StringdatabaseType){this.databaseType=databaseType;}publicStringgetDatabaseType(){returndatabaseType;}publicStringgetLimitBefore(){return"";}publicvoidsetLimitBefore(StringlimitBefore){}}

再自己项目里创建一个上述的类，问题解决