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target is null for method trim ???求大佬

### Error querying database. Cause: java.lang.NullPointerException: target is null for method trim

### Cause: java.lang.NullPointerException: target is null for method trim

at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:26)

at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:111)

at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:102)

at org.apache.ibatis.binding.MapperMethod.executeForMany(MapperMethod.java:119)

at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:63)

at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:52)

at com.sun.proxy.$Proxy8.queryMessageList(Unknown Source)

at com.imooc.dao.MessageDao.queryMessageList(MessageDao.java:39)

at com.imooc.service.QueryService.queryMessageList(QueryService.java:36)

at com.imooc.servlet.ListServlet.doGet(ListServlet.java:50)

at com.imooc.servlet.ListServlet.doPost(ListServlet.java:64)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:650)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)

at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)

at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:218)

at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:110)

at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:506)

at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)

at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)

at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:962)

at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)

at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:445)

at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1115)

at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637)

at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2549)

at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:2538)

at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)

at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)

at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)

at java.lang.Thread.run(Unknown Source)

Caused by: java.lang.NullPointerException: target is null for method trim

at org.apache.ibatis.ognl.OgnlRuntime.callMethod(OgnlRuntime.java:862)

at org.apache.ibatis.ognl.ASTMethod.getValueBody(ASTMethod.java:73)