private static <T> Bytes toBytesOrNull(T t, Function<T, byte[]> f) {
      if (t == null) {
        return null;
      } else {
        return new Bytes(f.apply(t));
      }
    }
Setter for storing metadata as a (key, value) pair in {@link #values} map
@param key   The key.
@param value The value. If null, removes the setting.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/TableDescriptorBuilder.java