500 Internal Error

java.lang.IllegalArgumentException: Object must not be null
	at org.jsoup.helper.Validate.notNull(Validate.java:16)
	at org.jsoup.nodes.Element.text(Element.java:953)
	at com.mandragola.mkwebsite.STArticleVideoGalleryItem.lambda$new$209(STArticleVideoGalleryItem.java:59)
	at java.util.Optional.ifPresent(Optional.java:159)
	at com.mandragola.mkwebsite.STArticleVideoGalleryItem.(STArticleVideoGalleryItem.java:59)
	at com.mandragola.mkwebsite.STArticleVideoGallery.(STArticleVideoGallery.java:25)
	at com.mandragola.mkwebsite.ArticoliController.lambda$doArticolo$44(ArticoliController.java:214)
	at java.util.Optional.ifPresent(Optional.java:159)
	at com.mandragola.mkwebsite.ArticoliController.doArticolo(ArticoliController.java:207)
	at com.mandragola.mkwebsite.ArticoliController.lambda$setupRoutes$37(ArticoliController.java:57)
	at spark.RouteImpl$1.handle(RouteImpl.java:58)
	at spark.webserver.MatcherFilter.doFilter(MatcherFilter.java:162)
	at com.mandragola.mkwebsite.MySparkFilter.doFilter(MySparkFilter.java:82)
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1668)
	at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:581)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)
	at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:548)
	at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:226)
	at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1158)
	at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:511)
	at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:185)
	at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1090)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
	at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:213)
	at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:109)
	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:119)
	at org.eclipse.jetty.server.Server.handle(Server.java:517)
	at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:308)
	at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:242)
	at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:273)
	at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:95)
	at org.eclipse.jetty.io.SelectChannelEndPoint$2.run(SelectChannelEndPoint.java:75)
	at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.produceAndRun(ExecuteProduceConsume.java:213)
	at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.run(ExecuteProduceConsume.java:147)
	at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:654)
	at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:572)
	at java.lang.Thread.run(Thread.java:745)