I've just installed JSPWiki for this domain. (I have an older version running on a different domain on the same Tomcat but different tomcat host and context.) When I try to save any page, I get the following NullPointerException:

 java.lang.NullPointerException
       at com.ecyrd.jspwiki.filters.FilterManager.fireEvent(FilterManager.java:361)
       at com.ecyrd.jspwiki.filters.FilterManager.doPreTranslateFiltering(FilterManager.java:268)
       at com.ecyrd.jspwiki.WikiEngine.textToHTML(WikiEngine.java:1371)
       at com.ecyrd.jspwiki.WikiEngine.saveText(WikiEngine.java:1567)
       at org.apache.jsp.Edit_jsp._jspService(org.apache.jsp.Edit_jsp:216)
       at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
       at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
       at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:322)
       at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:291)

Problem turned out to be caused by the jspwiki.fileSystemProvider.pageDir directory being owned by root instead of tomcat. A simple chown solved the problem.