EntryEditor now also shows on empty entries (#12955)

* EntryEditor now also shows on empty entries

* Fix entry editor showing "random" entry

* More _ for unused variables

* Fix Markdown

Author: koppor

docs/requirements/entry-editor.md

@@ -0,0 +1,15 @@
+---
+parent: Requirements
+---
+# Entry Editor
+
+## Entry Editor should show the last entry
+`req~entry-editor.keep-showing~1`
+
+The Entry Editor should "always" show a valid entry.
+
+When users search or select a group not containing the entry shown in the Entry Editor, the Entry Editor should keep showing until user select a new entry explicitly.
+
+Needs: impl
+
+<!-- markdownlint-disable-file MD022 -->

src/main/java/org/jabref/gui/entryeditor/EntryEditor.java

@@ -169,17 +169,19 @@ public EntryEditor(Supplier<LibraryTab> tabSupplier, UndoAction undoAction, Redo
             }
         });
 
-        stateManager.getSelectedEntries().addListener((InvalidationListener) c -> {
+        stateManager.getSelectedEntries().addListener((InvalidationListener) _ -> {
                     if (stateManager.getSelectedEntries().isEmpty()) {
-                        setCurrentlyEditedEntry(new BibEntry());
+                        // [impl->req~entry-editor.keep-showing~1]
+                        // No change in the entry editor
+                        // We allow users to edit the "old" entry
                     } else {
                         setCurrentlyEditedEntry(stateManager.getSelectedEntries().getFirst());
                     }
                 }
         );
 
         EasyBind.listen(preferences.getPreviewPreferences().showPreviewAsExtraTabProperty(),
-                (obs, oldValue, newValue) -> {
+                (_, _, newValue) -> {
                     if (currentlyEditedEntry != null) {
                         adaptVisibleTabs();
                         Tab tab = tabbed.getSelectionModel().selectedItemProperty().get();
@@ -425,14 +427,12 @@ public void setCurrentlyEditedEntry(@NonNull BibEntry currentlyEditedEntry) {
             typeSubscription.unsubscribe();
         }
 
-        if (!currentlyEditedEntry.isEmpty()) {
-            typeSubscription = EasyBind.subscribe(this.currentlyEditedEntry.typeProperty(), _ -> {
-                typeLabel.setText(new TypedBibEntry(currentlyEditedEntry, tabSupplier.get().getBibDatabaseContext().getMode()).getTypeForDisplay());
-                adaptVisibleTabs();
-                setupToolBar();
-                getSelectedTab().notifyAboutFocus(currentlyEditedEntry);
-            });
-        }
+        typeSubscription = EasyBind.subscribe(this.currentlyEditedEntry.typeProperty(), _ -> {
+            typeLabel.setText(new TypedBibEntry(currentlyEditedEntry, tabSupplier.get().getBibDatabaseContext().getMode()).getTypeForDisplay());
+            adaptVisibleTabs();
+            setupToolBar();
+            getSelectedTab().notifyAboutFocus(currentlyEditedEntry);
+        });
 
         if (preferences.getEntryEditorPreferences().showSourceTabByDefault()) {
             tabbed.getSelectionModel().select(sourceTab);