Support zip generation fails if nexus.log file is not called "nexus.log"

If the name of the nexus.log file is changed in the "logback.xml" file:

<File>/var/log/nexus3/nexus3.log</File>

Then this will prevent generation of a support zip file:

2018-11-06 17:08:59,672+0000 WARN [qtp1032748576-49] admin org.sonatype.nexus.internal.atlas.customizers.InstallConfigurationCustomizer - Skipping: /var/lib/nexus3/etc/fabric/hazelcast-network.xml
2018-11-06 17:09:00,926+0000 WARN [qtp1032748576-49] admin org.sonatype.nexus.internal.log.LogbackLogManager - Log file does not exist: nexus.log
2018-11-06 17:09:00,936+0000 ERROR [qtp1032748576-49] admin org.sonatype.nexus.internal.atlas.SupportZipGeneratorImpl - Failed to create support ZIP
java.lang.NullPointerException: Cannot invoke method withStream() on null object
at org.codehaus.groovy.runtime.NullObject.invokeMethod(NullObject.java:91)
at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.call(PogoMetaClassSite.java:47)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:47)
at org.codehaus.groovy.runtime.callsite.NullCallSite.call(NullCallSite.java:34)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:47)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:116)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:128)
at org.sonatype.nexus.internal.atlas.customizers.LogCustomizer$1.generate(LogCustomizer.groovy:63)
at org.sonatype.nexus.supportzip.GeneratedContentSourceSupport.prepare(GeneratedContentSourceSupport.java:51)
at org.sonatype.nexus.supportzip.SupportBundle$ContentSource$prepare.call(Unknown Source)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:47)
at org.sonatype.nexus.supportzip.SupportBundle$ContentSource$prepare.call(Unknown Source)
at org.sonatype.nexus.internal.atlas.SupportZipGeneratorImpl$_generate_closure3.doCall(SupportZipGeneratorImpl.groovy:181)
at sun.reflect.GeneratedMethodAccessor167.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:98)

 Expected:  The support zip code should take the name of the log file from the logback configuration, and use that when attempting to open the file.