log4j error at startup. This can be fixed by replacing log4j version 1.2.8 in WEB-INF/lib with current 1.2.14.

INFO: No jspwiki.propertyfile defined for this context, using default from /WEB-INF/jspwiki.properties
log4j:ERROR Error occured while converting date.
java.lang.NullPointerException
        at java.lang.AbstractStringBuilder.append(Unknown Source)
        at java.lang.StringBuffer.append(Unknown Source)
        at org.apache.log4j.helpers.ISO8601DateFormat.format(ISO8601DateFormat.java:124)
        at java.text.DateFormat.format(Unknown Source)
        at org.apache.log4j.helpers.PatternParser$DatePatternConverter.convert(PatternParser.java:436)
        at org.apache.log4j.helpers.PatternConverter.format(PatternConverter.java:56)
        at org.apache.log4j.PatternLayout.format(PatternLayout.java:495)
        at org.apache.log4j.WriterAppender.subAppend(WriterAppender.java:292)
        at org.apache.log4j.RollingFileAppender.subAppend(RollingFileAppender.java:225)
        at org.apache.log4j.WriterAppender.append(WriterAppender.java:150)
        at org.apache.log4j.AppenderSkeleton.doAppend(AppenderSkeleton.java:221)
        at org.apache.log4j.helpers.AppenderAttachableImpl.appendLoopOnAppenders(AppenderAttachableImpl.java:57)
        at org.apache.log4j.Category.callAppenders(Category.java:187)
        at org.apache.log4j.Category.forcedLog(Category.java:372)
        at org.apache.log4j.Category.error(Category.java:303)
        at com.ecyrd.jspwiki.util.WikiBackgroundThread.run(WikiBackgroundThread.java:153)
Exception in thread "WatchDog for 'MyWiki'" java.lang.NullPointerException
        at org.apache.log4j.NDC.get(NDC.java:201)
        at org.apache.log4j.spi.LoggingEvent.getNDC(LoggingEvent.java:229)
        at org.apache.log4j.helpers.PatternParser$BasicPatternConverter.convert(PatternParser.java:393)
        at org.apache.log4j.helpers.PatternConverter.format(PatternConverter.java:56)
        at org.apache.log4j.PatternLayout.format(PatternLayout.java:495)
        at org.apache.log4j.WriterAppender.subAppend(WriterAppender.java:292)
        at org.apache.log4j.RollingFileAppender.subAppend(RollingFileAppender.java:225)
        at org.apache.log4j.WriterAppender.append(WriterAppender.java:150)
        at org.apache.log4j.AppenderSkeleton.doAppend(AppenderSkeleton.java:221)
        at org.apache.log4j.helpers.AppenderAttachableImpl.appendLoopOnAppenders(AppenderAttachableImpl.java:57)
        at org.apache.log4j.Category.callAppenders(Category.java:187)
        at org.apache.log4j.Category.forcedLog(Category.java:372)
        at org.apache.log4j.Category.error(Category.java:303)
        at com.ecyrd.jspwiki.util.WikiBackgroundThread.run(WikiBackgroundThread.java:153)