getting error " is not a SuggestField"

[Vitaly Stroutchkov]

Hi,

I created a Lucene index with documents that have a SuggestField. When I run a 
completion query against it I'm getting an error.
The code is like this (not so straightforward in the actual program):

                                File sdir = new File(sgstPath);
                                Directory sgstDirectory = new 
MapDirectory(sdir.toPath());
                                Analyzer sgstAnalyzer = new StandardAnalyzer();
                                IndexWriterConfig sgstConfig = new 
IndexWriterConfig(sgstAnalyzer);
                                sgstConfig.setOpenMode(OpenMode.CREATE);
                                IndexWriter sgstWriter = new 
IndexWriter(sgstDirectory, sgstConfig);

                                ArrayList<Document> docs = new ArrayList<>();
                                Document doc = new Document();
                                doc.add(new SuggestField("$suggest", "suggest 
field content", 1));
                                docs.add(doc);
                                sgstWriter.addDocuments(docs);
                                sgstWriter.commit();
                                sgstWriter.close();

                                DirectoryReader sgstReader = 
DirectoryReader.open(sgstDirectory);
                                SuggestIndexSearcher sgstSearcher = new 
SuggestIndexSearcher(sgstReader);
                                CompletionQuery query = new 
FuzzyCompletionQuery(sgstAnalyzer, new Term("$suggest", "sug"));
                                TopSuggestDocs docs = 
sgstSearcher.suggest(query, 10, true);

On the last row I'm getting exception "$suggest is not a SuggestField". What 
can be a problem?

Thank you,
Vitaly