NPE if src of image is null in QTI 2.1

https://openolat.xyz.ch/auth/RepositoryEntry/58195968/Editor/0 ^%^ Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; rv:11.0) like Gecko
>>>stack of 1.cause::java.lang.NullPointerException: null
-> at org.olat.ims.qti21.ui.components.AssessmentRenderFunctions.convertLink(AssessmentRenderFunctions.java:619)
   at org.olat.ims.qti21.ui.components.AssessmentRenderFunctions.getHtmlAttributeValue(AssessmentRenderFunctions.java:584)
   at org.olat.ims.qti21.ui.components.AssessmentObjectComponentRenderer.renderHtmlTag(AssessmentObjectComponentRenderer.java:651)
   at org.olat.ims.qti21.ui.components.AssessmentObjectComponentRenderer.renderInline(AssessmentObjectComponentRenderer.java:537)
   at org.olat.ims.qti21.ui.components.AssessmentObjectComponentRenderer.lambda$renderBlock$6(AssessmentObjectComponentRenderer.java:370)
   at java.util.ArrayList.forEach(ArrayList.java:1249)
   at org.olat.ims.qti21.ui.components.AssessmentObjectComponentRenderer.renderBlock(AssessmentObjectComponentRenderer.java:369)
   at org.olat.ims.qti21.ui.components.AssessmentItemComponentRenderer.lambda$renderTestItemBody$0(AssessmentItemComponentRenderer.java:170)
   at java.util.ArrayList.forEach(ArrayList.java:1249)
   at org.olat.ims.qti21.ui.components.AssessmentItemComponentRenderer.renderTestItemBody(AssessmentItemComponentRenderer.java:169)
   at org.olat.ims.qti21.ui.components.AssessmentItemComponentRenderer.renderItemEvent(AssessmentItemComponentRenderer.java:143)