Cannot add poster in video resource of a Youtube film

2019-05-07 16:00:50,304 [ajp-nio2-8001-exec-8] ERROR OLATRuntimeException - OLAT::ERROR ^%^ N1-E2 ^%^ org.olat.core.logging 
https://xyz.olat.com/auth/RepositoryEntry/429588484/Editor/0/poster/0 ^%^ Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:66.0) Gecko/20100101 Firefox/66.0
**RedScreen**

<dispatchinfo>
	<componentinfo>
		<compname>ffo_main_null</compname>
		<compclass>org.olat.core.gui.components.form.flexible.impl.FormWrapperContainer</compclass>
		<extendedinfo>n/a</extendedinfo>
		<event>
			<class&gt;org.olat.core.gui.control.Event</class&gt;
			<command>validation ok</command>
			<tostring>com:validation ok,org.olat.core.gui.control.Event@d62b3f02</tostring>
		</event>
	</componentinfo>
	<controllerinfo>
		<controllername>org.olat.modules.video.ui.VideoPosterUploadForm</controllername>
		<controllername>org.olat.modules.video.ui.VideoPosterEditController</controllername>
		<controllername>org.olat.modules.video.ui.VideoSettingsController</controllername>
		<controllername>org.olat.modules.video.ui.VideoRuntimeController</controllername>
		<controllername>org.olat.core.commons.fullWebApp.BaseFullWebappController</controllername>
	</controllerinfo>
</dispatchinfo>

>>> stack of 1.cause::org.olat.core.logging.OLATRuntimeException: null
-> at org.olat.core.gui.exception.ExceptionWindowController.<init>(ExceptionWindowController.java:116)
   at org.olat.core.gui.exception.MsgFactory.createMessageChiefController(MsgFactory.java:57)
   at org.olat.core.gui.exception.MsgFactory.createMessageChiefController(MsgFactory.java:46)
   at org.olat.core.gui.components.Window.dispatchRequest(Window.java:589)
   at org.olat.core.gui.components.Window.doDispatchRequest(Window.java:282)
   at org.olat.core.gui.components.AbstractComponent.dispatchRequest(AbstractComponent.java:193)
   at org.olat.dispatcher.AuthenticatedDispatcher.processValidDispatchURI(AuthenticatedDispatcher.java:273)
   at org.olat.dispatcher.AuthenticatedDispatcher.execute(AuthenticatedDispatcher.java:190)
   at org.olat.core.servlets.OpenOLATServlet.executeUserRequest(OpenOLATServlet.java:294)
   at org.olat.core.servlets.OpenOLATServlet.doPost(OpenOLATServlet.java:237)
   at javax.servlet.http.HttpServlet.service(HttpServlet.java:661)
>>> stack of 2.cause::java.lang.NullPointerException: null
-> at org.olat.modules.video.manager.VideoManagerImpl.setPosterframeResizeUploadfile(VideoManagerImpl.java:194)
   at org.olat.modules.video.ui.VideoPosterEditController.event(VideoPosterEditController.java:122)
   at org.olat.core.gui.control.DefaultController$1.run(DefaultController.java:250)
   at org.olat.core.logging.activity.ThreadLocalUserActivityLoggerInstaller.runWithUserActivityLogger(ThreadLocalUserActivityLoggerInstaller.java:108)
   at org.olat.core.gui.control.DefaultController.dispatchEvent(DefaultController.java:247)
   at org.olat.core.gui.control.DefaultController.fireEvent(DefaultController.java:194)
   at org.olat.modules.video.ui.VideoPosterUploadForm.formOK(VideoPosterUploadForm.java:99)
   at org.olat.core.gui.components.form.flexible.impl.FormBasicController.event(FormBasicController.java:388)
   at org.olat.core.gui.control.DefaultController.dispatchEvent(DefaultController.java:206)
   at org.olat.core.gui.components.AbstractComponent$1.run(AbstractComponent.java:240)
   at org.olat.core.logging.activity.ThreadLocalUserActivityLoggerInstaller.runWithUserActivityLogger(ThreadLocalUserActivityLoggerInstaller.java:108)