code: public static <TKey, TValue> MultivaluedMap<TKey, TValue>
              putAll(MultivaluedMap<TKey, TValue> target, Map<TKey, TValue[]> data)
      {
          if (target == null || data == null)
          {
              return target;
          }
  
          for (Map.Entry<TKey, TValue[]> entry : data.entrySet())
          {
              target.addAll(entry.getKey(), entry.getValue());
          }
  
          return target;
      }
docs: Put all entries in a {@code Map<TKey, TValue[]>} instance
  into an existing {@code MultivaluedMap<TKey, TValue>}.
  
  @param target
  Target {@code MultivaluedMap} instance.
  
  @param data
  Input data.
  
  @return
  The object given as {@code target}.