code: private ComputingCache<String, Optional<String>> buildSourceCache() {
          return buildCache("Source",
                  key ->
                          Optional.ofNullable(locateAndRead(key)),
                  (key, cause) ->
                          LOGGER.debug("Removed template source from cache [templateId: {}, cause: {}]", key, cause));
      }
docs: Properties of the source cache are dependent on that of the template
  cache.