I have been following a course on Udemy using GeoServer (my version is 2.12.0). I plug in the same SQL code used in the course but when I click "Guess SQL Parameters", this message shows up:
org.apache.wicket.WicketRuntimeException: Exception in rendering component: [WebMarkupContainer [Component id = selectItemContainer]]
Perhaps it has something to do with Java? This morning I went to start GeoServer and it wouldn't start, so I looked at the startup.bat file and it was looking for a Java file that disappeared from my computer somehow (it wanted Java/jre1.8.0_73; I had jre1.8.0_71 and had just installed jre1.8.0_151, so I changed it to the latter and it started up just fine, but the error message seems to suggest that it's Java related.