public Optional<String> getSideInputsProcessorFactory(String storeName) {
    return Optional.ofNullable(get(String.format(SIDE_INPUTS_PROCESSOR_FACTORY, storeName)));
  }
Gets the SideInputsProcessorFactory associated with the {@code storeName}.

@param storeName name of the store
@return the class name of SideInputsProcessorFactory if present, empty optional otherwise
samza-core/src/main/java/org/apache/samza/config/StorageConfig.java