Merge branch 'feature/error-message-for-idno' into 'develop'

more custom errors

See merge request !68

modules/fontane/index-processor.xqm

@@ -5,7 +5,7 @@ xquery version "3.1";
 : the index for a single notebook.
 : The corresponding viewer module is `index-viewer.xqm`.
 : @author Mathias Göbel
-: @version 1.1.2
+: @version 1.1.3
 : @see https://fontane-nb.dariah.eu/register.html
 :)
 module namespace ixp="http://fontane-nb.dariah.eu/index-processor";
@@ -255,6 +255,10 @@ if(not(exists($variant))) then () else
 declare function ixp:idno($idnos as element()*)
 as element(xhtml:li)* {
 for $idno in $idnos
+where string-length($idno) lt 1
+return
+    error(QName("FONTANE", "INDEX3"), "got empty ID in element: " || serialize($idno/parent::tei:* ) ),
+for $idno in $idnos
 let $str := string($idno)
 let $wikipedia :=
   if($idno/@type = "GND") then ixp:gnd-wikipedia($str) else