tds/src/main/java/thredds/core/TdsRequestedDataset.java
public CoverageCollection openAsCoverageDataset(HttpServletRequest request, HttpServletResponse response) throws IOException {
    return datasetManager.openCoverageDataset(request, response, path);
  }
public CoverageCollection openAsCoverageDataset(HttpServletRequest request, HttpServletResponse response) throws IOException {
    return datasetManager.openCoverageDataset(request, response, path);
  }
return null means request has been handled, and calling routine should exit without further processing