code: private Object invokeMapper(File source) throws IOException {
          Object[] results;
          String name;
          Reader src;
  
          name = source.getPath();
          mork.output.verbose("mapping " + name);
          results = run(name);
          mork.output.verbose("finished mapping " + name);
          if (results == null) {
              return null;
          } else {
              return results[0];
          }
      }
docs: Read input. Wraps mapper.read with Mork-specific error handling.
  Return type depends on the mapper actually used.
  
  @return  null if an error has been reported