docs: public synchronized XmlNamespaceDictionary set(String alias, String uri) {
      String previousUri = null;
      String previousAlias = null;
      if (uri == null) {
        if (alias != null) {
          previousUri = namespaceAliasToUriMap.remove(alias);
        }
      } else if (alias == null) {
        previousAlias = namespaceUriToAliasMap.remove(uri);
      } else {
        previousUri =
            namespaceAliasToUriMap.put(
                Preconditions.checkNotNull(alias), Preconditions.checkNotNull(uri));
        if (!uri.equals(previousUri)) {
          previousAlias = namespaceUriToAliasMap.put(uri, alias);
        } else {
          previousUri = null;
        }
      }
      if (previousUri != null) {
        namespaceUriToAliasMap.remove(previousUri);
      }
      if (previousAlias != null) {
        namespaceAliasToUriMap.remove(previousAlias);
      }
      return this;
    }