code: public static Ix<String> split(String string, String by) {
          return new IxSplit(nullCheck(string, "string is null"), nullCheck(by, "by is null"));
      }
docs: Emits a sequence of substring of a string split by the given separator.
  <p>
  The result's iterator() doesn't support remove().
  @param string the string to split, not null
  @param by the separator to split along, not null
  @return the new Ix instance
  @throws NullPointerException if string or by is null
  @since 1.0