code: @Nonnull
      public static <K, V> Map<K, V> putAll(@Nonnull Map<K, V> original, @Nullable Object... a) {
          if (a != null) {
              final int length = a.length;
              if (length % 2 == 1) {
                  throw new IllegalArgumentException("You must provide an even number of arguments.");
              }
              for (int i = 0; i < length; i += 2) {
                  // noinspection unchecked
                  original.put((K) a[i], (V) a[i + 1]);
              }
          }
          return original;
      }
docs: Returns a the given map enriched
  with the mappings <code>a[0] => a[1], a[2] => a[3], ...</code>.
  @param a the elements to construct a {@link Map} from.
  @return a {@link Map} constructed of the specified elements.