Xinha Image Variant always needs to be choosen

If the preferred image variant is not or not proper configured, the insert image dialog of the xinha editor is producing a NPE if no variant is selected.

28.03.2011 12:35:49 ERROR [org.apache.wicket.RequestCycle.logRuntimeException():1529]
java.lang.NullPointerException
at org.hippoecm.frontend.plugins.xinha.model.DocumentLink.isSameType(DocumentLink.java:82)
at org.hippoecm.frontend.plugins.xinha.services.images.XinhaImageService$1.save(XinhaImageService.java:92)
at org.hippoecm.frontend.plugins.xinha.dialog.images.ImageBrowserDialog.onOk(ImageBrowserDialog.java:359)
at org.hippoecm.frontend.dialog.AbstractDialog.handleSubmit(AbstractDialog.java:580)
at org.hippoecm.frontend.dialog.AbstractDialog$3.onSubmit(AbstractDialog.java:430)
at org.hippoecm.frontend.dialog.AbstractDialog$ButtonWrapper$1.onSubmit(AbstractDialog.java:251)
at org.apache.wicket.ajax.markup.html.form.AjaxButton$1.onSubmit(AjaxButton.java:101)
at org.apache.wicket.ajax.form.AjaxFormSubmitBehavior.onEvent(AjaxFormSubmitBehavior.java:143)
at org.apache.wicket.ajax.AjaxEventBehavior.respond(AjaxEventBehavior.java:177)