Error 500 on single EPUB

Added a new EPUB to the server, but it won't load. Thought it might be the file, but it loads in a desktop EPUB Reader program just fine. Haven't had this kind of error so far.

Here's the page that loads:

HTTP ERROR 500
Problem accessing /epubreader/68/. Reason:
Internal server error: null

Here's the log:

20191107 15:53:55 [qtp1739063-24507] ERROR com.ubooquity.d.b - Request processing failed for URI: /epubreader/68/?opening=true (method:GET)
java.lang.NullPointerException: null
   at com.ubooquity.fileformat.epub.c.close(SourceFile:242) ~[Ubooquity.jar:2.1.2]
   at com.ubooquity.f.b.a(SourceFile:21) ~[Ubooquity.jar:2.1.2]
   at com.ubooquity.provider.epubreader.a.a(SourceFile:145) ~[Ubooquity.jar:2.1.2]
   at com.ubooquity.d.c.a(SourceFile:142) ~[Ubooquity.jar:2.1.2]
   at com.ubooquity.d.b.handle(SourceFile:54) ~[Ubooquity.jar:2.1.2]
   at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132) [jetty-server-9.4.0.v20161208.jar.1383638551838216221.tmp:9.4.0.v20161208]
   at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:190) [jetty-server-9.4.0.v20161208.jar.1383638551838216221.tmp:9.4.0.v20161208]
   at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1228) [jetty-server-9.4.0.v20161208.jar.1383638551838216221.tmp:9.4.0.v20161208]
   at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:170) [jetty-server-9.4.0.v20161208.jar.1383638551838216221.tmp:9.4.0.v20161208]
   at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1130) [jetty-server-9.4.0.v20161208.jar.1383638551838216221.tmp:9.4.0.v20161208]
   at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141) [jetty-server-9.4.0.v20161208.jar.1383638551838216221.tmp:9.4.0.v20161208]
   at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:118) [jetty-server-9.4.0.v20161208.jar.1383638551838216221.tmp:9.4.0.v20161208]
   at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132) [jetty-server-9.4.0.v20161208.jar.1383638551838216221.tmp:9.4.0.v20161208]
   at org.eclipse.jetty.server.Server.handle(Server.java:564) [jetty-server-9.4.0.v20161208.jar.1383638551838216221.tmp:9.4.0.v20161208]
   at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:318) [jetty-server-9.4.0.v20161208.jar.1383638551838216221.tmp:9.4.0.v20161208]
   at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:251) [jetty-server-9.4.0.v20161208.jar.1383638551838216221.tmp:9.4.0.v20161208]
   at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:279) [jetty-io-9.4.0.v20161208.jar.8575756471483478842.tmp:9.4.0.v20161208]
   at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:112) [jetty-io-9.4.0.v20161208.jar.8575756471483478842.tmp:9.4.0.v20161208]
   at org.eclipse.jetty.io.ChannelEndPoint$2.run(ChannelEndPoint.java:124) [jetty-io-9.4.0.v20161208.jar.8575756471483478842.tmp:9.4.0.v20161208]
   at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:672) [jetty-util-9.4.0.v20161208.jar.5478157055240233035.tmp:9.4.0.v20161208]
   at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:590) [jetty-util-9.4.0.v20161208.jar.5478157055240233035.tmp:9.4.0.v20161208]
   at java.lang.Thread.run(Unknown Source) [na:1.8.0_221]