Fix unmodifable Set Exception in generating preview

Add hint in javadoc

Fixes #9947
Fixes JabRef/jabref-issue-melting-pot#183

CHANGELOG.md

@@ -90,6 +90,7 @@ Note that this project **does not** adhere to [Semantic Versioning](http://semve
 - We fixed an issue in the preferences where custom columns could be added to the entry table with no qualifier. [#9913](https://github.com/JabRef/jabref/issues/9913)
 - We fixed an issue where the encoding header in a bib file was not respected when the file contained a BOM (Byte Order Mark). [#9926](https://github.com/JabRef/jabref/issues/9926)
 - We fixed an issue where cli help output for import and export format was inconsistent. [koppor#429](https://github.com/koppor/jabref/issues/429)
+- We fixed an issue where no preview could be generated for some entry types and led to an exception [#9947](https://github.com/JabRef/jabref/issues/9947)
 
 ### Removed
 

src/main/java/org/jabref/logic/citationstyle/JabRefItemDataProvider.java

@@ -2,6 +2,7 @@
 
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Locale;
 import java.util.Optional;
@@ -147,7 +148,7 @@ private CSLItemData bibEntryToCSLItemData(BibEntry originalBibEntry, BibDatabase
             }
         }
 
-        Set<Field> fields = entryType.map(BibEntryType::getAllFields).orElse(bibEntry.getFields());
+        Set<Field> fields = new LinkedHashSet<>(entryType.map(BibEntryType::getAllFields).orElse(bibEntry.getFields()));
         fields.addAll(bibEntry.getFields());
         for (Field key : fields) {
             bibEntry.getResolvedFieldOrAlias(key, bibDatabaseContext.getDatabase())

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

@@ -313,7 +313,7 @@ public Optional<String> getResolvedFieldOrAliasLatexFree(Field field, BibDatabas
     }
 
     private Optional<String> genericGetResolvedFieldOrAlias(Field field, BibDatabase database, BiFunction<BibEntry, Field, Optional<String>> getFieldOrAlias) {
-        if (InternalField.TYPE_HEADER == field || InternalField.OBSOLETE_TYPE_HEADER == field) {
+        if ((InternalField.TYPE_HEADER == field) || (InternalField.OBSOLETE_TYPE_HEADER == field)) {
             return Optional.of(type.get().getDisplayName());
         }
 
@@ -434,7 +434,7 @@ public Optional<FieldChange> setType(EntryType newType, EntriesEventSource event
     }
 
     /**
-     * Returns a set containing the names of all fields that are set for this particular entry.
+     * Returns an {@link Collections#unmodifiableSet(Set)} containing the names of all fields that are set for this particular entry.
      *
      * @return a set of existing field names
      */
@@ -489,7 +489,7 @@ private Optional<String> genericGetFieldOrAlias(Field field, BiFunction<BibEntry
             return date.map(Date::getNormalized);
         }
 
-        if (StandardField.YEAR == field || StandardField.MONTH == field || StandardField.DAY == field) {
+        if ((StandardField.YEAR == field) || (StandardField.MONTH == field) || (StandardField.DAY == field)) {
             Optional<String> date = getFieldValue.apply(this, StandardField.DATE);
             if (date.isEmpty()) {
                 return Optional.empty();