I tried to upgrade my test Jenkins instance from 1.480.3 to 1.525.

On startup, I got this:

org.jvnet.hudson.reactor.ReactorException: hudson.util.IOException2: Unable to read /var/lib/jenkins/config.xml
at org.jvnet.hudson.reactor.Reactor.execute(Reactor.java:246)
at jenkins.InitReactorRunner.run(InitReactorRunner.java:43)
at jenkins.model.Jenkins.executeReactor(Jenkins.java:906)
at jenkins.model.Jenkins.<init>(Jenkins.java:806)
at hudson.model.Hudson.<init>(Hudson.java:81)
at hudson.model.Hudson.<init>(Hudson.java:77)
at hudson.WebAppMain$2.run(WebAppMain.java:214)
Caused by: hudson.util.IOException2: Unable to read /var/lib/jenkins/config.xml
at hudson.XmlFile.unmarshal(XmlFile.java:170)
at jenkins.model.Jenkins$17.run(Jenkins.java:2526)
at org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:146)
at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:259)
at jenkins.model.Jenkins$7.runTask(Jenkins.java:895)
at org.jvnet.hudson.reactor.Reactor$2.run(Reactor.java:187)
at org.jvnet.hudson.reactor.Reactor$Node.run(Reactor.java:94)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:898)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:920)
at java.lang.Thread.run(Thread.java:736)
Caused by: com.thoughtworks.xstream.converters.ConversionException: Array index out of range: -1 : Array index out of range: -1
---- Debugging information ----
message : Array index out of range: -1
cause-exception : java.lang.ArrayIndexOutOfBoundsException
cause-message : Array index out of range: -1
class : hudson.model.Hudson
required-type : hudson.model.Hudson
converter-type : hudson.util.RobustReflectionConverter
path : /hudson/disabledAdministrativeMonitors
line number : 3
version : null
-------------------------------
at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:79)
at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:65)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:66)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:50)
at com.thoughtworks.xstream.core.TreeUnmarshaller.start(TreeUnmarshaller.java:134)
at com.thoughtworks.xstream.core.AbstractTreeMarshallingStrategy.unmarshal(AbstractTreeMarshallingStrategy.java:32)
at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:1061)
at hudson.util.XStream2.unmarshal(XStream2.java:109)
at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:1045)
at hudson.XmlFile.unmarshal(XmlFile.java:166)
... 9 more
Caused by: java.lang.ArrayIndexOutOfBoundsException: Array index out of range: -1
at com.thoughtworks.xstream.core.util.OrderRetainingMap.entrySet(OrderRetainingMap.java:77)
at java.util.HashMap.putAllImpl(HashMap.java:678)
at java.util.HashMap.putAll(HashMap.java:669)
at com.thoughtworks.xstream.core.util.OrderRetainingMap.<init>(OrderRetainingMap.java:36)
at com.thoughtworks.xstream.converters.reflection.FieldDictionary.buildMap(FieldDictionary.java:135)
at com.thoughtworks.xstream.converters.reflection.FieldDictionary.fieldOrNull(FieldDictionary.java:113)
at com.thoughtworks.xstream.converters.reflection.PureJavaReflectionProvider.getFieldOrNull(PureJavaReflectionProvider.java:186)
at hudson.util.RobustReflectionConverter.fieldDefinedInClass(RobustReflectionConverter.java:328)
at hudson.util.RobustReflectionConverter.doUnmarshal(RobustReflectionConverter.java:269)
at hudson.util.RobustReflectionConverter.unmarshal(RobustReflectionConverter.java:222)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:72)
... 18 more