NPE when creating pivot

I get a NPE, the trace is shown at the end.

The problem seems to be this line in the getSubset method:
Query query = ft.getFieldQuery(null, field, pivotValue);

Which takes a value from the index and then analyses it to create a query. I believe the problem is that when my analysis process is applied twice it results in a null query. OK this might be seen as my issue because of dodgy analysis, I thought it might be because I have the wrong order with LengthFilterFactory before EnglishPossessiveFilterFactory and KStemFilterFactory, i.e.:
<filter class="solr.LengthFilterFactory" min="3" max="32"/>
<filter class="solr.EnglishPossessiveFilterFactory"/>
<filter class="solr.KStemFilterFactory"/>

So that "cat's" -> "cat" -> "", however any filter order I tried still resulted in a NPE, and perhaps there is a viable case where parsing a term twice results in a null query.

The thing is I don't see why when the query term comes from the index it has to undergo any analysis. If the term is from the index can it not simply be created using a TermQuery, which I would imagine would also be faster. I altered the "getFieldQuery" line above to the following and that has fixed my NPE issue.

Query query = new TermQuery(new Term(field.getName(), pivotValue));

So far this hasn't caused any other issues but perhaps that is due to my use of Solr, rather than actually fixing an issue.

o.a.s.c.SolrCore java.lang.NullPointerException
at java.util.concurrent.ConcurrentHashMap.get(ConcurrentHashMap.java:936)
at org.apache.solr.util.ConcurrentLRUCache.get(ConcurrentLRUCache.java:91)
at org.apache.solr.search.FastLRUCache.get(FastLRUCache.java:130)
at org.apache.solr.search.SolrIndexSearcher.getDocSet(SolrIndexSearcher.java:1296)
at org.apache.solr.handler.component.PivotFacetProcessor.getSubset(PivotFacetProcessor.java:375)
at org.apache.solr.handler.component.PivotFacetProcessor.doPivots(PivotFacetProcessor.java:305)
at org.apache.solr.handler.component.PivotFacetProcessor.processSingle(PivotFacetProcessor.java:228)
at org.apache.solr.handler.component.PivotFacetProcessor.process(PivotFacetProcessor.java:170)
at org.apache.solr.handler.component.FacetComponent.process(FacetComponent.java:262)
at org.apache.solr.handler.component.SearchHandler.handleRequestBody(SearchHandler.java:277)
at org.apache.solr.handler.RequestHandlerBase.handleRequest(RequestHandlerBase.java:143)
at org.apache.solr.core.SolrCore.execute(SolrCore.java:2068)
at org.apache.solr.servlet.HttpSolrCall.execute(HttpSolrCall.java:669)
at org.apache.solr.servlet.HttpSolrCall.call(HttpSolrCall.java:462)
at org.apache.solr.servlet.SolrDispatchFilter.doFilter(SolrDispatchFilter.java:214)
at org.apache.solr.servlet.SolrDispatchFilter.doFilter(SolrDispatchFilter.java:179)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1652)
at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:585)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)
at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:577)
at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:223)
at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1127)
at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:515)
at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:185)
at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1061)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:215)
at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:110)
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:97)
at org.eclipse.jetty.server.Server.handle(Server.java:499)
at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:310)
at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:257)
at org.eclipse.jetty.io.AbstractConnection$2.run(AbstractConnection.java:540)
at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:635)
at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:555)
at java.lang.Thread.run(Thread.java:745)