code: public static <T> T checkNotNull (T value, String param)
      {
          if (value == null) {
              throw new NullPointerException("Must supply non-null '" + param + "'.");
          }
          return value;
      }
docs: Checks that the supplied parameter is not null. Throws a {@link NullPointerException} if it
  is, using the supplied `param` string to include an informative error message.