[Copy] Copy referenced constant strings to clipboard (#16)

* feat: Add parsed serialized string when cloning
* feat: Add sanity check for null in ClipBoardManager
* closes #15

Author: JXNCTED

src/main/java/org/jabref/gui/ClipBoardManager.java

@@ -171,11 +171,7 @@ public void setContent(List<BibEntry> entries, BibEntryTypesManager entryTypesMa
         final ClipboardContent content = new ClipboardContent();
         BibEntryWriter writer = new BibEntryWriter(new FieldWriter(preferencesService.getFieldPreferences()), entryTypesManager);
         StringBuilder builder = new StringBuilder();
-        for (BibtexString strConst : stringConstants) {
-            if (strConst.getParsedSerialization() != null) {
-                builder.append(strConst.getParsedSerialization());
-            }
-        }
+        stringConstants.forEach(strConst -> builder.append(strConst.getParsedSerialization() == null ? "" : strConst.getParsedSerialization()));
         String serializedEntries = writer.serializeAll(entries, BibDatabaseMode.BIBTEX);
         builder.append(serializedEntries);
         // BibEntry is not Java serializable. Thus, we need to do the serialization manually

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

@@ -258,8 +258,7 @@ public void copy() {
         List<BibEntry> selectedEntries = getSelectedEntries();
 
         if (!selectedEntries.isEmpty()) {
-            List<BibtexString> stringConstants = getStringValues();
-
+            List<BibtexString> stringConstants = getUsedStringValues(selectedEntries);
             try {
                 if (!stringConstants.isEmpty()) {
                     clipBoardManager.setContent(selectedEntries, entryTypesManager, stringConstants);
@@ -497,10 +496,7 @@ private Optional<BibEntryTableViewModel> findEntry(BibEntry entry) {
                     .findFirst();
     }
 
-    private List<BibtexString> getStringValues() {
-        return database.getDatabase()
-                       .getStringValues()
-                       .stream()
-                       .toList();
+    private List<BibtexString> getUsedStringValues(List<BibEntry> entries) {
+        return database.getDatabase().getUsedStrings(entries).stream().toList();
     }
 }

src/main/java/org/jabref/model/entry/BibtexString.java

@@ -158,6 +158,9 @@ public String getUserComments() {
     public Object clone() {
         BibtexString clone = new BibtexString(name, content);
         clone.setId(id);
+        if (parsedSerialization != null) {
+            clone.setParsedSerialization(parsedSerialization);
+        }
 
         return clone;
     }