Another "system has attempted to use an undefined value" problem

I'm a little embarassed to post this since I've recently posted something very similar, but this really is a different set of circumstances. I have a site running on ColdFusion 11 (v. 11,0,19,314546) without incident. As soon as I move it to ColdFusion 2018 (v. 2018.0.11.326016), without changing any code, I get the message "The system has attempted to use an undefined value, which usually indicates a programming error, either in your code or some system code. Null Pointers are another name for undefined values."

This is on my local machine. I've tried rebooting, restarting ColdFusion, running in different browsers, clearing all cookies - no success. I've stepped through each line of my "onApplicationStart" block with <cfabort/> and everything is fine. When I add <cfabort/> as the first line within my "onRequestStart" block, I get the error. (There is no "onSessionStart" code, this is a fairly old site..)

The site uses session management:

<cfscript>
this.name = "cntsPhones";
this.applicationTimeout = CreateTimeSpan(1,0,0,0);
this.sessionManagement = true;
this.sessionTimeout = CreateTimeSpan(0,0,30,0);
</cfscript>

Are there any common gotchas when moving from CF 11 to this version of CF 2018 that could explain this problem?

Here's the stack trace:

java.lang.NullPointerException
	at coldfusion.runtime.AppHelper.generateNewClientIDs(AppHelper.java:605)
	at coldfusion.runtime.AppHelper.handleClientIDs(AppHelper.java:221)
	at coldfusion.runtime.AppHelper.ValidateClientAndSession(AppHelper.java:1239)
	at coldfusion.filter.ApplicationFilter.invoke(ApplicationFilter.java:483)
	at coldfusion.filter.RequestMonitorFilter.invoke(RequestMonitorFilter.java:43)
	at coldfusion.filter.MonitoringFilter.invoke(MonitoringFilter.java:40)
	at coldfusion.filter.PathFilter.invoke(PathFilter.java:162)
	at coldfusion.filter.IpFilter.invoke(IpFilter.java:45)
	at coldfusion.filter.LicenseFilter.invoke(LicenseFilter.java:30)
	at coldfusion.filter.ExceptionFilter.invoke(ExceptionFilter.java:96)
	at coldfusion.filter.BrowserDebugFilter.invoke(BrowserDebugFilter.java:78)
	at coldfusion.filter.ClientScopePersistenceFilter.invoke(ClientScopePersistenceFilter.java:28)
	at coldfusion.filter.BrowserFilter.invoke(BrowserFilter.java:38)
	at coldfusion.filter.NoCacheFilter.invoke(NoCacheFilter.java:60)
	at coldfusion.filter.GlobalsFilter.invoke(GlobalsFilter.java:38)
	at coldfusion.filter.DatasourceFilter.invoke(DatasourceFilter.java:22)
	at coldfusion.filter.CachingFilter.invoke(CachingFilter.java:62)
	at coldfusion.CfmServlet.service(CfmServlet.java:226)
	at coldfusion.bootstrap.BootstrapServlet.service(BootstrapServlet.java:311)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at coldfusion.monitor.event.MonitoringServletFilter.doFilter(MonitoringServletFilter.java:46)
	at coldfusion.bootstrap.BootstrapFilter.doFilter(BootstrapFilter.java:47)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at coldfusion.inspect.weinre.MobileDeviceDomInspectionFilter.doFilter(MobileDeviceDomInspectionFilter.java:121)
	at coldfusion.bootstrap.BootstrapFilter.doFilter(BootstrapFilter.java:47)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:143)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:359)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:888)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1597)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.base/java.lang.Thread.run(Thread.java:834)

Any suggestions are welcome, I'm at a loss. Thank you!