docs: private Map<String, SignerConfig> mergeSignerMap(JsonIndex<SignerConfigJsonHelper, SignerConfig>[] defaults,
                                                       JsonIndex<SignerConfigJsonHelper, SignerConfig>[] overrides,
                                                       String theme) {
          Map<String, SignerConfig> map = buildSignerMap(defaults, theme);
          Map<String, SignerConfig> mapOverride = buildSignerMap(overrides, theme);
          map.putAll(mapOverride);
          return Collections.unmodifiableMap(map);
      }