FULL PRODUCT VERSION :
Java version: 1.8.0_60, Oracle Corporation, Java HotSpot(TM) 64-Bit Server VM

VM arguments: [-Djava.security.manager, -Djava.security.policy=file:C:\Program Files\Java\jre1.8.0_60\lib\security\javaws.policy, -DtrustProxy=true, -Djnlpx.home=<java.home>\bin, -Djnlpx.origFilenameArg=C:\Users\<XXX>\AppData\LocalLow\Sun\Java\Deployment\cache\6.0\56\1ee8cfb8-44547ac1, -Djnlpx.remove=false, -Djava.util.Arrays.useLegacyMergeSort=true, -Djnlpx.splashport=59276, -Djnlp.application.href=https://josm.openstreetmap.de/download/josm.jnlp, -Djnlpx.jvm=<java.home>\bin\javaw.exe, -Djnlpx.vmargs=LURqYXZhLnV0aWwuQXJyYXlzLnVzZUxlZ2FjeU1lcmdlU29ydD10cnVlAC1Eam5scC5hcHBsaWNhdGlvbi5ocmVmPWh0dHBzOi8vam9zbS5vcGVuc3RyZWV0bWFwLmRlL2Rvd25sb2FkL2pvc20uam5scAA=]


ADDITIONAL OS VERSION INFORMATION :
Windows 7 32-Bit
Windows 7 64-Bit

A DESCRIPTION OF THE PROBLEM :
This is an upstream bug report for this issue reported two times for JOSM:
https://josm.openstreetmap.de/ticket/11743
https://josm.openstreetmap.de/ticket/11946

Users face an NPE when Java Web Start seems to try to clear the cache, as the stacktrace makes us think.

It may be linked to the usage of -Djava.util.Arrays.useLegacyMergeSort=true

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Launch JOSM in JNLP: https://josm.openstreetmap.de/download/josm.jnlp

The JNLP defines the property -Djava.util.Arrays.useLegacyMergeSort=true

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
JOSM starts without error.
ACTUAL -
Java Web Start crashes.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
two different stacktraces.

this one for 8u51:
java.lang.NullPointerException
at com.sun.deploy.cache.CacheEntry.removeBefore(Unknown Source)
at com.sun.deploy.cache.CleanupThread$2.compare(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.legacyMergeSort(Unknown Source)
at java.util.Arrays.sort(Unknown Source)
at com.sun.deploy.cache.CleanupThread.prepareRemovalList(Unknown Source)
at com.sun.deploy.cache.CleanupThread.run(Unknown Source)

This one for 8u60:
java.lang.NullPointerException
at com.sun.deploy.cache.CleanupThread$2.compare(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.mergeSort(Unknown Source)
at java.util.Arrays.legacyMergeSort(Unknown Source)
at java.util.Arrays.sort(Unknown Source)
at com.sun.deploy.cache.CleanupThread.prepareRemovalList(Unknown Source)
at com.sun.deploy.cache.CleanupThread.run(Unknown Source)

REPRODUCIBILITY :
This bug can be reproduced rarely.

---------- BEGIN SOURCE ----------
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE jnlp PUBLIC "-//Sun Microsystems, Inc//DTD JNLP Descriptor 6.0//EN" "http://java.sun.com/dtd/JNLP-6.0.dtd">
<jnlp spec="6.0+" codebase="https://josm.openstreetmap.de/download/" href="josm.jnlp">
    <information>
        <title>JOSM</title>
        <vendor>OpenStreetMap</vendor>
        <homepage href="https://josm.openstreetmap.de"/>
        <description>Java OpenStreetMap editor</description>
        <description kind="one-line">JOSM</description>
        <description kind="tooltip">JOSM</description>
        <icon href="https://josm.openstreetmap.de/svn/trunk/images/logo.png"/>
        <offline-allowed/>
        <shortcut>
            <desktop/>
            <menu/>
        </shortcut>
    </information>
    <security>
        <all-permissions/>
    </security>
    <resources>
        <j2se version="1.7+"/>
        <jar href="josm-tested.jar"/>
        <property name="java.util.Arrays.useLegacyMergeSort" value="true"/>
    </resources>
    <application-desc main-class="JOSM"/>
</jnlp>

---------- END SOURCE ----------