@Override
 public List<FieldChange> remove(List<BibEntry> entriesToRemove) {
   Objects.requireNonNull(entriesToRemove);
   List<FieldChange> changes = new ArrayList<>();
   for (BibEntry entry : entriesToRemove) {
     if (contains(entry)) {
       String oldContent = entry.getField(searchField).orElse("");
       KeywordList wordlist = KeywordList.parse(oldContent, keywordSeparator);
       wordlist.remove(searchExpression);
       String newContent = wordlist.getAsString(keywordSeparator);
       entry.setField(searchField, newContent).ifPresent(changes::add);
     }
   }
   return changes;
 }
 private Set<String> getFieldContentAsWords(BibEntry entry) {
   if (onlySplitWordsAtSeparator) {
     return entry
         .getField(searchField)
         .map(content -> KeywordList.parse(content, keywordSeparator).toStringList())
         .orElse(Collections.emptySet());
   } else {
     return entry.getFieldAsWords(searchField);
   }
 }