lucene的writer.addDocument（）报空指针

[艺术的姿态]

writer.addDocument(doc); 报nullpoint，是怎么回事啊
getDocument(file)具体代码：

//获取文档，文档里再设置每个字段，就类似于数据库中的一行记录
    private Document getDocument(File file) throws Exception{
        Document doc = new Document();
        //添加字段
        doc.add(new TextField("contents", new FileReader(file))); //添加内容
        doc.add(new TextField("fileName", file.getName(), Field.Store.YES)); //添加文件名，并把这个字段存到索引文件里
        doc.add(new TextField("fullPath", file.getCanonicalPath(), Field.Store.YES)); //添加文件路径
        return doc;
    }

报错信息：

java.lang.NullPointerException
	at org.apache.lucene.analysis.standard.StandardTokenizer.init(StandardTokenizer.java:144)
	at org.apache.lucene.analysis.standard.StandardTokenizer.<init>(StandardTokenizer.java:131)
	at org.apache.lucene.analysis.standard.StandardAnalyzer.createComponents(StandardAnalyzer.java:111)
	at org.apache.lucene.analysis.Analyzer.tokenStream(Analyzer.java:142)
	at org.apache.lucene.document.Field.tokenStream(Field.java:550)
	at org.apache.lucene.index.DocInverterPerField.processFields(DocInverterPerField.java:95)
	at org.apache.lucene.index.DocFieldProcessor.processDocument(DocFieldProcessor.java:248)
	at org.apache.lucene.index.DocumentsWriterPerThread.updateDocument(DocumentsWriterPerThread.java:253)
	at org.apache.lucene.index.DocumentsWriter.updateDocument(DocumentsWriter.java:453)
	at org.apache.lucene.index.IndexWriter.updateDocument(IndexWriter.java:1520)
	at org.apache.lucene.index.IndexWriter.addDocument(IndexWriter.java:1190)
	at org.apache.lucene.index.IndexWriter.addDocument(IndexWriter.java:1171)
	at Indexer.indexFile(Indexer.java:49)
	at Indexer.indexAll(Indexer.java:39)
	at Indexer.main(Indexer.java:70)