Small fix to VarMMPreset variable when presets list is empty

src/main/java/plugins/stef/micromanager/block/lang/VarMMPreset.java

@@ -55,5 +55,7 @@ public class VarMMPreset extends VarString
         if (presets.size() > 0)
             setDefaultEditorModel(new ValueSelectionModel<String>(presets.toArray(new String[presets.size()]),
                     presets.get(0), false));
+        else 
+            setDefaultEditorModel(new ValueSelectionModel<String>(new String[] {""}, "", false));
     }
 }