SchematicSelector.renderItem can not be null

SpigotCore_Main/src/de/steamwar/inventory/SchematicSelector.java

@@ -235,6 +235,10 @@ public class SchematicSelector {
     private SWListInv.SWListEntry<SchematicNode> renderItem(SchematicNode node) {
         Material m = SWItem.getMaterial(node.getItem());
 
+        if(m == null) {
+            m = Material.AIR;
+        }
+
         String name = Core.MESSAGE.parse(filter.name == null?"SCHEM_SELECTOR_ITEM_NAME":"SCHEM_SELECTOR_ITEM_NAME_FILTER", player, node.getName());
 
         if(filter.getName() != null) {