/// <summary>
 /// Creates a new instance initialized with the given stopword set
 /// </summary>
 /// <param name="version">
 ///          the Lucene version for cross version compatibility </param>
 /// <param name="stopwords">
 ///          the analyzer's stopword set </param>
 protected internal StopwordAnalyzerBase(Version version, CharArraySet stopwords)
 {
     matchVersion = version;
     // analyzers should use char array set for stopwords!
     this.stopwords = stopwords == null ? CharArraySet.EMPTY_SET : CharArraySet.unmodifiableSet(CharArraySet.Copy(version, stopwords));
 }