Fix: exception dialog shows up when moving sidepanel down/up (JabRef#15248)

* fix exception dialog when moving panel down/up

* update CHANGELOG.md

* Apply suggestion from @Siedlerchr

Co-authored-by: Christoph <siedlerkiller@gmail.com>

* Stylistic change

---------

Co-authored-by: Christoph <siedlerkiller@gmail.com>
Co-authored-by: Carl Christian Snethlage <calixtus@users.noreply.github.com>
Co-authored-by: Carl Christian Snethlage <50491877+calixtus@users.noreply.github.com>

Author: 3 people

CHANGELOG.md

@@ -27,6 +27,7 @@ Note that this project **does not** adhere to [Semantic Versioning](https://semv
 ### Fixed
 
 - We fixed an issue where pressing ESC now properly closes the global search dialog. [#15133](https://github.com/JabRef/jabref/issues/15133)
+- We fixed an issue where an exception dialog was shown when moving side panels down/up. [#15207](https://github.com/JabRef/jabref/issues/15207)
 - We fixed a false "Invalid citation key" warning for keys with diacritical marks. [#14953](https://github.com/JabRef/jabref/issues/14953)
 - We fixed an issue where duplicate fields can be created. [#15130](https://github.com/JabRef/jabref/issues/15130)
 - We fixed an issue where blank fields could be created. [#15130](https://github.com/JabRef/jabref/issues/15130)

jabgui/src/main/java/org/jabref/gui/frame/SidePanePreferences.java

@@ -1,5 +1,6 @@
 package org.jabref.gui.frame;
 
+import java.util.EnumMap;
 import java.util.EnumSet;
 import java.util.Map;
 import java.util.Set;
@@ -20,8 +21,10 @@ public class SidePanePreferences {
     public SidePanePreferences(Set<SidePaneType> visiblePanes,
                                Map<SidePaneType, Integer> preferredPositions,
                                int webSearchFetcherSelected) {
-        this.visiblePanes = FXCollections.observableSet(visiblePanes);
-        this.preferredPositions = FXCollections.observableMap(preferredPositions);
+        this.visiblePanes = FXCollections.observableSet(EnumSet.noneOf(SidePaneType.class));
+        this.visiblePanes.addAll(visiblePanes);
+        this.preferredPositions = FXCollections.observableMap(new EnumMap<>(SidePaneType.class));
+        this.preferredPositions.putAll(preferredPositions);
         this.webSearchFetcherSelected = new SimpleIntegerProperty(webSearchFetcherSelected);
     }