Target is null for setProperty (NULL,) cause of error and resolution

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Error message:

Warning: Error setting expression ' USER.UPW ' with value ' [ljava.lang.string;@6581a654 ' OGNL. Ognlexception:target is null for setProperty (null, ' UPW ', [ljava.lang.string;@6581a654) at OGNL. Ognlruntime.setproperty (ognlruntime.java:2309) at OGNL. Astproperty.setvaluebody (astproperty.java:127) at OGNL. Simplenode.evaluatesetvaluebody (simplenode.java:220) at OGNL. Simplenode.setvalue (simplenode.java:301) at OGNL. Astchain.setvaluebody (astchain.java:227) at OGNL. Simplenode.evaluatesetvaluebody (simplenode.java:220) at OGNL. Simplenode.setvalue (simplenode.java:301) at OGNL. Ognl.setvalue (ognl.java:737) at Com.opensymphony.xwork2.ognl.OgnlUtil.setValue (ognlutil.java:217) at Com.opensymphony.xwork2.ognl.OgnlValueStack.trySetValue (ognlvaluestack.java:186) at Com.opensymphony.xwork2.ognl.OgnlValueStack.setValue (ognlvaluestack.java:173) at Com.opensymphony.xwork2.ognl.OgnlValueStack.setParameter (ognlvaluestack.java:151) at Com.opensymphony.xwork2.interceptor.ParametersInterceptor.setParameters (Parametersinterceptor.java:317) at Com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept ( parametersinterceptor.java:228) at Com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept ( methodfilterinterceptor.java:98) at Com.opensymphony.xwork2.DefaultActionInvocation.invoke ( defaultactioninvocation.java:249) at Com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept ( parametersinterceptor.java:236) at Com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept ( methodfilterinterceptor.java:98) at Com.opensymphony.xwork2.DefaultActionInvocation.invoke ( defaultactioninvocation.java:249) at Com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept ( staticparametersinterceptor.java:190) at Com.opensymphony.xwork2.DefaultActionInvocation.invoke ( defaultactioninvocation.java:249) at Org.apache.struts2.interceptor.MultiselectInterceptor.intercept ( multiselectinterceptor.java:75) at Com.opensymphony.xwork2.DefaultActionInvocatIon.invoke (defaultactioninvocation.java:249) at Org.apache.struts2.interceptor.CheckboxInterceptor.intercept ( CHECKBOXINTERCEPTOR.JAVA:90) at Com.opensymphony.xwork2.DefaultActionInvocation.invoke ( defaultactioninvocation.java:249) at Org.apache.struts2.interceptor.FileUploadInterceptor.intercept ( fileuploadinterceptor.java:243) at Com.opensymphony.xwork2.DefaultActionInvocation.invoke ( defaultactioninvocation.java:249) at Com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept ( modeldriveninterceptor.java:100) at Com.opensymphony.xwork2.DefaultActionInvocation.invoke ( defaultactioninvocation.java:249) at Com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept ( scopedmodeldriveninterceptor.java:141) at Com.opensymphony.xwork2.DefaultActionInvocation.invoke ( defaultactioninvocation.java:249) at Com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept ( chaininginterceptor.java:145) at Com.opensymphony.xwork2.DefaultActionInvocation.invoke (Defaultactioninvocation.java:249) at Com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept ( prepareinterceptor.java:171) at Com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept ( methodfilterinterceptor.java:98) at Com.opensymphony.xwork2.DefaultActionInvocation.invoke ( defaultactioninvocation.java:249) at Com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept ( i18ninterceptor.java:176) at Com.opensymphony.xwork2.DefaultActionInvocation.invoke (Defaultactioninvocation.java : 249) at Org.apache.struts2.interceptor.ServletConfigInterceptor.intercept (servletconfiginterceptor.java:164) at Com.opensymphony.xwork2.DefaultActionInvocation.invoke (defaultactioninvocation.java:249) at Com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept (aliasinterceptor.java:192) at Com.opensymphony.xwork2.DefaultActionInvocation.invoke (defaultactioninvocation.java:249) at Com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept (exceptionmappinginterceptor.java:187) at Com.opensymphony.xwork2.DefaultActionInvocation.invoke (defaultactioninvocation.java:249) at Org.apache.struts2.impl.StrutsActionProxy.execute (strutsactionproxy.java:54) at Org.apache.struts2.dispatcher.Dispatcher.serviceAction (dispatcher.java:511) at Org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction (executeoperations.java:77) at Org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter ( strutsprepareandexecutefilter.java:91) 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:220) at Org.apache.catalina.core.StandardContextValve.invoke (Standardcontextvalve.java : 122) at Org.apache.catalina.authenticator.AuthenticatorBase.invoke (authenticatorbase.java:503) at Org.apache.catalina.core.StandardHostValve.invokE (standardhostvalve.java:170) at Org.apache.catalina.valves.ErrorReportValve.invoke (errorreportvalve.java:103) at Org.apache.catalina.valves.AccessLogValve.invoke (accesslogvalve.java:950) at Org.apache.catalina.core.StandardEngineValve.invoke (standardenginevalve.java:116) at Org.apache.catalina.connector.CoyoteAdapter.service (coyoteadapter.java:421) at Org.apache.coyote.http11.AbstractHttp11Processor.process (abstracthttp11processor.java:1070) at Org.apache.coyote.abstractprotocol$abstractconnectionhandler.process (abstractprotocol.java:611) at Org.apache.tomcat.util.net.jioendpoint$socketprocessor.run (jioendpoint.java:316) at Java.util.concurrent.ThreadPoolExecutor.runWorker (threadpoolexecutor.java:1145) at Java.util.concurrent.threadpoolexecutor$worker.run (threadpoolexecutor.java:615) at Org.apache.tomcat.util.threads.taskthread$wrappingrunnable.run (taskthread.java:61) at Java.lang.Thread.run ( thread.java:744)

This error means that the object calling SetProperty () is empty.
This type of error is caused by using USER.UPW to the action in the JSP page, and the user object in the specified action is empty, so the value cannot be received.

When this error occurs, first check the Struts.xml configuration file to see if the specified action is wrong or if there is a name for the action.