refs #20834 [finc] add getItemCallnumber FincLibero

* overrides VuFind DAIA method
* set emtpy string for empty label instead of english word 'UNKNOWN'
* moved from de_15 and de_l152

module/finc/src/finc/ILS/Driver/FincLibero.php

@@ -454,6 +454,20 @@ class FincLibero extends FincILS implements TranslatorAwareInterface
         return $details;
     }
 
+    /**
+     * Returns the value for "callnumber" in VuFind getStatus/getHolding array
+     *
+     * @param array $item Array with DAIA item data
+     *
+     * @return string
+     */
+    protected function getItemCallnumber($item)
+    {
+        return isset($item['label']) && !empty($item['label'])
+            ? $item['label']
+            : '';
+    }
+
     /**
      * FincLibero specific overrides of DAIA methods
      */