// safe because both Long.class and long.class are of type Class
  @SuppressWarnings("unchecked")
  private static  Class wrap(Class c) {
    return c.isPrimitive() ? (Class) PRIMITIVES_TO_WRAPPERS.get(c) : c;
  }

  private static final Map, Class> PRIMITIVES_TO_WRAPPERS
    = new ImmutableMap.Builder, Class>()
      .put(boolean.class, Boolean.class)
      .put(byte.class, Byte.class)
      .put(char.class, Character.class)
      .put(double.class, Double.class)
      .put(float.class, Float.class)
      .put(int.class, Integer.class)
      .put(long.class, Long.class)
      .put(short.class, Short.class)
      .put(void.class, Void.class)
      .build();