Fix no such element exception in copy to (#12488)

* Fix np such element exception in copy tp

Fixes JabRef/jabref-issue-melting-pot#768

Follow up to #12374

* fix checkstyle

Author: Siedlerchr

src/main/java/org/jabref/gui/maintable/RightClickMenu.java

@@ -1,6 +1,5 @@
 package org.jabref.gui.maintable;
 
-import java.nio.file.Path;
 import java.util.Optional;
 
 import javax.swing.undo.UndoManager;
@@ -120,27 +119,31 @@ private static Menu createCopyToMenu(ActionFactory factory,
                                          StateManager stateManager,
                                          GuiPreferences preferences,
                                          LibraryTab libraryTab,
-                                         ImportHandler importHandler
-                                         ) {
+                                         ImportHandler importHandler) {
         Menu copyToMenu = factory.createMenu(StandardActions.COPY_TO);
 
         ObservableList<BibDatabaseContext> openDatabases = stateManager.getOpenDatabases();
 
         BibDatabaseContext sourceDatabaseContext = libraryTab.getBibDatabaseContext();
 
-        Optional<Path> sourcePath = libraryTab.getBibDatabaseContext().getDatabasePath();
-        String sourceDatabaseName = FileUtil.getUniquePathFragment(stateManager.collectAllDatabasePaths(), sourcePath.get()).get();
+        Optional<String> sourceDatabaseName = libraryTab
+                .getBibDatabaseContext().getDatabasePath().stream()
+                .flatMap(path -> FileUtil.getUniquePathFragment(stateManager.collectAllDatabasePaths(), path).stream())
+                .findFirst();
 
         if (!openDatabases.isEmpty()) {
             openDatabases.forEach(bibDatabaseContext -> {
                 Optional<String> destinationPath = Optional.empty();
                 String destinationDatabaseName = "";
 
                 if (bibDatabaseContext.getDatabasePath().isPresent()) {
-                    destinationDatabaseName = FileUtil.getUniquePathFragment(stateManager.collectAllDatabasePaths(), bibDatabaseContext.getDatabasePath().get()).get();
-                    if (destinationDatabaseName.equals(sourceDatabaseName)) {
+                    Optional<String> uniqueFilePathFragment = FileUtil.getUniquePathFragment(stateManager.collectAllDatabasePaths(), bibDatabaseContext.getDatabasePath().get());
+                    if (uniqueFilePathFragment.equals(sourceDatabaseName)) {
                         return;
                     }
+                    if (uniqueFilePathFragment.isPresent()) {
+                        destinationDatabaseName = uniqueFilePathFragment.get();
+                    }
                 } else if (bibDatabaseContext.getLocation() == DatabaseLocation.SHARED) {
                     destinationDatabaseName = bibDatabaseContext.getDBMSSynchronizer().getDBName() + " [" + Localization.lang("shared") + "]";
                 } else {