code: public void setPlusSignString(String plusSignString) {
          if (plusSignString == null) {
              throw new NullPointerException("The input plus sign is null");
          }
          this.plusString = plusSignString;
          if (plusSignString.length() == 1) {
              this.plusSign = plusSignString.charAt(0);
          } else {
              // Use the default plus sign as fallback
              this.plusSign = DEF_PLUS_SIGN;
          }
      }
docs: <strong>[icu]</strong> Sets the localized plus sign string.
  <p>
  <b>Note:</b> When the input plus sign String is represented
  by multiple Java chars, then {@link #getPlusSign()} will
  return the default plus sign character ('+').
  
  @param plusSignString the plus sign string, used in localized patterns and formatted
  strings
  @throws NullPointerException if <code>plusSignString</code> is null.
  @see #getPlusSignString()
  @hide draft / provisional / internal are hidden on Android