Error in match of numerical entry (FIB)

Business Pfad: https://testing.frentix.com/test8/url/VideoSite/0 Datum und Zeit: 16.02.2017 11:50 
2017-02-16 09:23:10,448 [ajp-nio-8028-exec-1] ERROR FIBAssessmentItemBuilder - OLAT::ERROR ^%^ N8-E2 
https://testing.frentix.com/test8/auth/RepositoryEntry/364150784/CourseNode/94254009965393
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_3) AppleWebKit/602.4.8 (KHTML, like Gecko) Version/10.0.3 Safari/602.4.8 ^%^
>>>stack of 1.cause::java.lang.NumberFormatException: empty String
-> at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1842)
   at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110)
   at java.lang.Double.parseDouble(Double.java:538)
   at org.olat.ims.qti21.model.xml.interactions.FIBAssessmentItemBuilder$NumericalEntry.match(FIBAssessmentItemBuilder.java:956)
   at org.olat.ims.qti21.manager.archive.interactions.TextEntryInteractionArchive.writeInteractionData(TextEntryInteractionArchive.java:58)
   at org.olat.ims.qti21.manager.archive.QTI21ArchiveFormat.writeDataRow(QTI21ArchiveFormat.java:446)
   at org.olat.ims.qti21.manager.archive.QTI21ArchiveFormat.writeData(QTI21ArchiveFormat.java:365) 
   t org.olat.ims.qti21.manager.archive.QTI21ArchiveFormat.exportWorkbook(QTI21ArchiveFormat.java:239)
   at org.olat.ims.qti21.manager.archive.QTI21ArchiveFormat.export(QTI21ArchiveFormat.java:218)
   at org.olat.ims.qti21.manager.archive.QTI21ArchiveFormat.exportCourseElement(QTI21ArchiveFormat.java:205)