Review

class SegmentReader {
  /** Return a term frequency vector for the specified document and field. The
   *  vector returned contains term numbers and frequencies for all terms in
   *  the specified field of this document, if the field had storeTermVector
   *  flag set.  If the flag was not set, the method returns null.
   * @throws IOException
   */
  public TermFreqVector getTermFreqVector(int docNumber, String field) throws IOException {
    // Check if this field is invalid or has no stored term vector
    ensureOpen();
    FieldInfo fi = core.fieldInfos.fieldInfo(field);
    if (fi == null || !fi.storeTermVector) 
      return null;
    
    TermVectorsReader termVectorsReader = getTermVectorsReader();
    if (termVectorsReader == null)
      return null;
    
    return termVectorsReader.get(docNumber, field);
  }

}