Upgrading to the July 2016 patch of Yellowfin can result in the following startup error if the Yellowfin server is not connected to the internet.
SEVERE: Servlet.service() for servlet [com.hof.jsp.index_005fmi_jsp] in context with path [/ctcopy] threw exception
java.lang.NullPointerException: Module 'null' not found.
at org.apache.struts.taglib.TagUtils.getModuleConfig(TagUtils.java:755)
The July 2016 build of Yellowfin includes a Struts upgrade, which introduced this behavior. The reason that this error pops up is because the system searches for a specific necessary dtd file locally, which it is unable to find. When it cannot find the file locally, it attempts to download it from the Struts website. If the server is not connected to the internet, the Struts website will not be accessible, Struts will not initialize successfully, and the startup process will fail.
Solutions:
1) Upgrade to the August 2016 release
2) Connect the Yellowfin server to the internet. This will allow the necessary file to be downloaded on startup so that Struts can be started successfully.
3) Place the .jar file from the bottom of this post in the folder <YourYellowfinDirectory>/appserver/webapps/ROOT/WEB-INF/lib. The attached .jar file contains the necessary dtd file for Struts initialization, so Yellowfin won't have to go search for it.