code: private Map<String, Object> injectGlobalOptionsFallback(
        final Version version, final Manifest manifest, final String name,
        final Map<String, Object> options) {
      final Map<String, Object> copy = new HashMap<String, Object>(options);
      copy.put("version", version.toString());
      if (manifest != null) {
        if ("merge".equals(name)) {
          copy.put("source", GlobalOptions.isSourceOnce(manifest) ? "once" : "");
        }
      }
      return copy;
    }
docs: This is a migration method for global to processor options. Currently used
  by the merge-processor which gets the 'source:once' option from the global
  scope.