Unresolvable site and NPE when log4j config is not specified

In a standalone tomcat installation, not specifying the system property log4j.configuration leads to NPE and an unresolvable site.

The NPE:

og4j:WARN No appenders could be found for logger (org.hippoecm.frontend.Main).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
SLF4J: Failed toString() invocation on an object of type [org.hippoecm.hst.core.hosting.CustomMountAndVirtualCmsHostAugmenter$CustomMount]
java.lang.NullPointerException
at org.hippoecm.hst.core.hosting.CustomMountAndVirtualCmsHostAugmenter$CustomMount.toString(CustomMountAndVirtualCmsHostAugmenter.java:791)
at org.slf4j.helpers.MessageFormatter.safeObjectAppend(MessageFormatter.java:304)
at org.slf4j.helpers.MessageFormatter.deeplyAppendParameter(MessageFormatter.java:276)
at org.slf4j.helpers.MessageFormatter.arrayFormat(MessageFormatter.java:230)
at org.slf4j.helpers.MessageFormatter.format(MessageFormatter.java:124)
at org.slf4j.impl.Log4jLoggerAdapter.debug(Log4jLoggerAdapter.java:228)
at org.hippoecm.hst.configuration.channel.ChannelManagerImpl.load(ChannelManagerImpl.java:306)
at org.hippoecm.hst.configuration.model.HstManagerImpl.buildSites(HstManagerImpl.java:546)
at org.hippoecm.hst.configuration.model.HstManagerImpl.synchronousBuild(HstManagerImpl.java:390)
at org.hippoecm.hst.configuration.model.HstManagerImpl.getVirtualHosts(HstManagerImpl.java:366)
at org.hippoecm.hst.container.HstFilter.doFilter(HstFilter.java:286)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.hippoecm.hst.container.XSSUrlFilter.doFilter(XSSUrlFilter.java:49)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:947)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1009)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:724)