Template error

FreeMarker template error:
The following has evaluated to null or missing:
==> rewix.getQueryParam("error")  [in template "frontend/bmartigrafiche/login.ftl" at line 22, column 18]

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Tip: If the failing expression is known to legally refer to something that's sometimes null or missing, either specify a default value like myOptionalVar!myDefault, or use <#if myOptionalVar??>when-present<#else>when-missing</#if>. (These only cover the last step of the expression; to cover the whole expression, use parenthesis: (myOptionalVar.foo)!myDefault, (myOptionalVar.foo)??
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FTL stack trace ("~" means nesting-related):
	- Failed at: #global error = rewix.getQueryParam("...  [in template "frontend/bmartigrafiche/login.ftl" at line 22, column 1]
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Java stack trace (for programmers):
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freemarker.core.InvalidReferenceException: [... Exception message was already printed; see it above ...]
	at freemarker.core.InvalidReferenceException.getInstance(InvalidReferenceException.java:134)
	at freemarker.core.Assignment.accept(Assignment.java:139)
	at freemarker.core.Environment.visit(Environment.java:344)
	at freemarker.core.Environment.visit(Environment.java:350)
	at freemarker.core.Environment.process(Environment.java:323)
	at com.rewix.services.internal.RewixFreemarkerService.processCMSInstanceTemplate(RewixFreemarkerService.java:128)
	at com.rewix.services.internal.RewixFreemarkerService.processCMSInstanceTemplate(RewixFreemarkerService.java:113)
	at com.rewix.frontend.internal.RewixFrontendTemplateService.applyFreemarkerTemplate(RewixFrontendTemplateService.java:281)
	at com.rewix.frontend.internal.RewixFrontendTemplateService.applyTemplateInternal(RewixFrontendTemplateService.java:239)
	at com.rewix.frontend.handler.AbstractRequestHandler.applyTemplate(AbstractRequestHandler.java:179)
	at com.rewix.frontend.handler.AbstractRequestHandler.applyTemplate(AbstractRequestHandler.java:158)
	at com.rewix.frontend.handler.LoginRequestHandler.handleRequestInternal(LoginRequestHandler.java:117)
	at com.rewix.frontend.handler.AbstractRequestHandler.handleRequest(AbstractRequestHandler.java:91)
	at com.rewix.frontend.FrontendServlet.doGet(FrontendServlet.java:172)
	at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:578)
	at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:197)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:142)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:57)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:166)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:142)
	at com.rewix.frontend.filter.RewixGlobalErrorPageFilter.doFilter(RewixGlobalErrorPageFilter.java:46)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:166)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:142)
	at com.rewix.filter.LoginFilter.doFilter(LoginFilter.java:414)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:166)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:142)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:165)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:88)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:534)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:115)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:86)
	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:782)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:72)
	at org.apache.catalina.ha.session.JvmRouteBinderValve.invoke(JvmRouteBinderValve.java:178)
	at org.apache.catalina.ha.tcp.ReplicationValve.invoke(ReplicationValve.java:340)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:348)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:71)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:1307)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:2032)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:74)
	at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:976)
	at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:494)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:80)
	at java.base/java.lang.Thread.run(Thread.java:1474)