java - XML serializer error -

i getting following error when prepare document , return.

please find code below

        public static document requestparammissing (string params, string codeexception, string message, string apimethod, exception e, subscriberid, string udid, stringbuilder listparams, string requestid, string apiurl){      document doc = null;      string errorcodenumber = '';     documentbuilderfactory docfactory = documentbuilderfactory.newinstance();     documentbuilder docbuilder = docfactory.newdocumentbuilder();     doc = docbuilder.newdocument();     element rootelement = doc.createelement("error");     doc.appendchild(rootelement);     element errorcode = doc.createelement("code");     element errormessage = doc.createelement("message");     if(codeexception.equals('requestexception')){         errorcodenumber = '1000';         errorcode.appendchild(doc.createtextnode('1000'));         errormessage.appendchild(doc.createtextnode(message));     }else{         if(e?.tostring()?.contains('unknownhostexception')){             errorcodenumber = '2000';             errorcode.appendchild(doc.createtextnode('2000'));             errormessage.appendchild(doc.createtextnode('unknownhostexception'));         }else if(e?.tostring()?.contains('sockettimeoutexception')){             errorcodenumber = '3000';             errorcode.appendchild(doc.createtextnode('3000'));             errormessage.appendchild(doc.createtextnode('sockettimeoutexception'));         }else if(e?.tostring()?.contains('clientexception')){             errorcodenumber = '4000';             errorcode.appendchild(doc.createtextnode('4000'));             errormessage.appendchild(doc.createtextnode('clientexception'));         }else if(e?.tostring()?.contains('httpresponseexception')){             errorcodenumber = '5000';             errorcode.appendchild(doc.createtextnode('5000'));             errormessage.appendchild(doc.createtextnode("httpresponseexception"));         }else{             errorcodenumber = '6000';             errorcode.appendchild(doc.createtextnode('6000'));             errormessage.appendchild(doc.createtextnode(e.tostring()));         }     }      rootelement.appendchild(errorcode);     rootelement.appendchild(errormessage);      element errorapimethod = doc.createelement("apimethod");     errorapimethod.appendchild(doc.createtextnode(apimethod));     rootelement.appendchild(errorapimethod);      element errorapiurl = doc.createelement("apiurl");     errorapiurl.appendchild(doc.createtextnode(apiurl));     rootelement.appendchild(errorapiurl);      element errorexception = doc.createelement("exception");     if(e != null){         errorexception.appendchild(doc.createtextnode(e.tostring()));     }else{         errorexception.appendchild(doc.createtextnode(''));     }     rootelement.appendchild(errorexception);      element errormissingparam = doc.createelement("missingparamvalue");     errormissingparam.appendchild(doc.createtextnode(params));     rootelement.appendchild(errormissingparam);     logger.error('ef response time: errors [api request url method:' + apimethod + ';error code :' + errorcodenumber + ';status:' +             'failure in teleflora ' + apiurl +' request;params:' + listparams +';exception:' + e +             ';udid:' + udid + ';requestid:' + requestid + ']---> subscriberid:'+ subscriberid);      return doc; } 

error:

     java.lang.nullpointerexception @ org.apache.xml.serializer.treewalker.dispatachchars(treewalker.java:246) @ org.apache.xml.serializer.treewalker.startnode(treewalker.java:416) @ org.apache.xml.serializer.treewalker.traverse(treewalker.java:145) @ org.apache.xalan.transformer.transformeridentityimpl.transform(transformeridentityimpl.java:390) @ com.sun.jersey.core.impl.provider.entity.documentprovider.writeto(documentprovider.java:120) @ com.sun.jersey.core.impl.provider.entity.documentprovider.writeto(documentprovider.java:70) @ com.sun.jersey.spi.container.containerresponse.write(containerresponse.java:306) @ com.sun.jersey.server.impl.application.webapplicationimpl._handlerequest(webapplicationimpl.java:1437) @ com.sun.jersey.server.impl.application.webapplicationimpl.handlerequest(webapplicationimpl.java:1349) @ com.sun.jersey.server.impl.application.webapplicationimpl.handlerequest(webapplicationimpl.java:1339) @ com.sun.jersey.spi.container.servlet.webcomponent.service(webcomponent.java:416) @ com.sun.jersey.spi.container.servlet.servletcontainer.service(servletcontainer.java:537) @ com.sun.jersey.spi.container.servlet.servletcontainer.service(servletcontainer.java:708) @ javax.servlet.http.httpservlet.service(httpservlet.java:722) @ org.apache.catalina.core.applicationfilterchain.internaldofilter(applicationfilterchain.java:305) @ org.apache.catalina.core.applicationfilterchain.dofilter(applicationfilterchain.java:210) @ org.apache.catalina.core.standardwrappervalve.invoke(standardwrappervalve.java:225) @ org.apache.catalina.core.standardcontextvalve.invoke(standardcontextvalve.java:169) @ org.apache.catalina.authenticator.authenticatorbase.invoke(authenticatorbase.java:472) @ org.apache.catalina.core.standardhostvalve.invoke(standardhostvalve.java:168) @ org.apache.catalina.valves.errorreportvalve.invoke(errorreportvalve.java:98) @ org.apache.catalina.valves.accesslogvalve.invoke(accesslogvalve.java:927) @ org.apache.catalina.core.standardenginevalve.invoke(standardenginevalve.java:118) @ org.apache.catalina.connector.coyoteadapter.service(coyoteadapter.java:407) @ org.apache.coyote.http11.abstracthttp11processor.process(abstracthttp11processor.java:999) @ org.apache.coyote.abstractprotocol$abstractconnectionhandler.process(abstractprotocol.java:565) @ org.apache.tomcat.util.net.jioendpoint$socketprocessor.run(jioendpoint.java:309) @ java.util.concurrent.threadpoolexecutor$worker.runtask(unknown source) @ java.util.concurrent.threadpoolexecutor$worker.run(unknown source) @ java.lang.thread.run(unknown source) 

fwiw, it's caused appending null text value. check message not null. newer serializer may fix issue.