code: private Set<Comparable> prepareKeys(OIndex<?> index, Object keys) {
      final Class<?> targetType = index.getKeyTypes()[0].getDefaultJavaType();
  
      return convertResult(keys, targetType);
    }
docs: Make type conversion of keys for specific index.
  
  @param index
  - index for which keys prepared for.
  @param keys
  - which should be prepared.
  @return keys converted to necessary type.