code: private MaccsKey[] keys(final IChemObjectBuilder builder) throws CDKException {
          MaccsKey[] result = keys;
          if (result == null) {
              synchronized (lock) {
                  result = keys;
                  if (result == null) {
                      try {
                          keys = result = readKeyDef(builder);
                      } catch (IOException e) {
                          throw new CDKException("could not read MACCS definitions", e);
                      }
                  }
              }
          }
          return result;
      }
docs: Access MACCS keys definitions.
  
  @return array of MACCS keys.
  @throws CDKException maccs keys could not be loaded