disable conversions for empty fields (JabRef#9202)

* disable conversion menu for empty fields

* fix disabling of conversion menu

Co-authored-by: Patrick Helm <helm@synyx.de>

CHANGELOG.md

@@ -21,6 +21,7 @@ Note that this project **does not** adhere to [Semantic Versioning](http://semve
 
 ### Changed
 
+- We disabled the conversion menu for empty fields [#9200](https://github.com/JabRef/jabref/issues/9200)
 - We upgraded to Lucene 9.4 for the fulltext search.
   Thus, the now created search index cannot be read from older versions of JabRef anylonger.
   ⚠️ JabRef will recreate the index in a new folder for new files and this will take a long time for a huge library.

src/main/java/org/jabref/gui/fieldeditors/contextmenu/DefaultMenu.java

@@ -15,6 +15,9 @@
 import org.jabref.logic.cleanup.Formatter;
 import org.jabref.logic.formatter.Formatters;
 import org.jabref.logic.l10n.Localization;
+import org.jabref.model.strings.StringUtil;
+
+import com.tobiasdiez.easybind.EasyBind;
 
 public class DefaultMenu implements Supplier<List<MenuItem>> {
 
@@ -62,6 +65,7 @@ private static Menu getConversionMenu(TextInputControl textInputControl) {
             CustomMenuItem menuItem = new CustomMenuItem(new Label(converter.getName()));
             Tooltip toolTip = new Tooltip(converter.getDescription());
             Tooltip.install(menuItem.getContent(), toolTip);
+            EasyBind.subscribe(textInputControl.textProperty(), value -> menuItem.setDisable(StringUtil.isNullOrEmpty(value)));
             menuItem.setOnAction(event ->
                     textInputControl.textProperty().set(converter.format(textInputControl.textProperty().get())));
             submenu.getItems().add(menuItem);