docs: public void setIncludeFilter(File filterFile) {
          if (filterFile != null && filterFile.length() > 0) {
              includeFile = filterFile;
          } else {
              if (filterFile != null) {
                  log("Warning: include filter file " + filterFile
                          + (filterFile.exists() ? " is empty" : " does not exist"));
              }
              includeFile = null;
          }
      }