LTR FieldLengthFeature causes NullPointerException with documents that do not have the requested field

{
"initArgs": {},
"initializedOn": "2019-01-21T21:09:59.011Z",
"updatedSinceInit": "2019-01-21T22:01:14.113Z",
"managedList": [
{
"name": "descriptionLength",
"class": "org.apache.solr.ltr.feature.FieldLengthFeature",
"params": {
"field": "tm_my_fulltext_field"
},
"store": "_DEFAULT_"
}
]
}

http://localhost:8983/solr/dropsolid8/select?q=europe&json.nl=flat&omitHeader=true&fl=ss_search_api_id,ss_search_api_language,hash,[features]&start=0&rows=10&wt=json&rq={!ltr efi.query=europe model=originalScoreModel}}&df=tm_X3b_nl_rendered_item

2019-02-05 13:45:36.087 ERROR (qtp690521419-21) [ x:dropsolid8] o.a.s.h.RequestHandlerBase org.apache.solr.common.SolrException: java.lang.NullPointerException
at org.apache.solr.search.ReRankCollector.topDocs(ReRankCollector.java:140)
at org.apache.solr.search.SolrIndexSearcher.getDocListNC(SolrIndexSearcher.java:1607)
at org.apache.solr.search.SolrIndexSearcher.getDocListC(SolrIndexSearcher.java:1421)
at org.apache.solr.search.SolrIndexSearcher.search(SolrIndexSearcher.java:568)
at org.apache.solr.handler.component.QueryComponent.doProcessUngroupedSearch(QueryComponent.java:1435)
at org.apache.solr.handler.component.QueryComponent.process(QueryComponent.java:375)
at org.apache.solr.handler.component.SearchHandler.handleRequestBody(SearchHandler.java:298)
at org.apache.solr.handler.RequestHandlerBase.handleRequest(RequestHandlerBase.java:199)
at org.apache.solr.core.SolrCore.execute(SolrCore.java:2541)
at org.apache.solr.servlet.HttpSolrCall.execute(HttpSolrCall.java:709)
at org.apache.solr.servlet.HttpSolrCall.call(HttpSolrCall.java:515)
at org.apache.solr.servlet.SolrDispatchFilter.doFilter(SolrDispatchFilter.java:377)
at org.apache.solr.servlet.SolrDispatchFilter.doFilter(SolrDispatchFilter.java:323)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1634)
at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:533)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:146)
at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:548)
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:257)
at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:1595)
at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:255)
at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1317)
at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:203)
at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:473)
at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:1564)
at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:201)
at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1219)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:144)
at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:219)
at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:126)
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
at org.eclipse.jetty.rewrite.handler.RewriteHandler.handle(RewriteHandler.java:335)
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
at org.eclipse.jetty.server.Server.handle(Server.java:531)
at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:352)
at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:260)
at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:281)
at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:102)
at org.eclipse.jetty.io.ChannelEndPoint$2.run(ChannelEndPoint.java:118)
at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.runTask(EatWhatYouKill.java:333)
at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.doProduce(EatWhatYouKill.java:310)
at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.tryProduce(EatWhatYouKill.java:168)
at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.run(EatWhatYouKill.java:126)
at org.eclipse.jetty.util.thread.ReservedThreadExecutor$ReservedThread.run(ReservedThreadExecutor.java:366)
at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:762)
at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:680)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
at org.apache.solr.ltr.feature.FieldLengthFeature$FieldLengthFeatureWeight$FieldLengthFeatureScorer.<init>(FieldLengthFeature.java:134)
at org.apache.solr.ltr.feature.FieldLengthFeature$FieldLengthFeatureWeight.scorer(FieldLengthFeature.java:120)
at org.apache.solr.ltr.LTRScoringQuery$ModelWeight.scorer(LTRScoringQuery.java:467)
at org.apache.solr.ltr.LTRRescorer.scoreFeatures(LTRRescorer.java:164)
at org.apache.solr.ltr.LTRRescorer.rescore(LTRRescorer.java:119)
at org.apache.solr.search.ReRankCollector.topDocs(ReRankCollector.java:106)
... 46 more