code: @Override
      public JavaFileObject getOverviewPath() {
          if (overviewpath != null && getFileManager() instanceof StandardJavaFileManager) {
              StandardJavaFileManager fm = (StandardJavaFileManager) getFileManager();
              return fm.getJavaFileObjects(overviewpath).iterator().next();
          }
          return null;
      }
docs: Return the path of the overview file or null if it does not exist.
  
  @return the path of the overview file or null if it does not exist.