code: @Override
      public StringBuffer format(Object qty, StringBuffer toAppendTo, FieldPosition pos) {
          return format(qty, toAppendTo, pos, minimumFractionDigits, decimalGroups);
      }
docs: Formats a bitcoin value as a number and possibly a units indicator and appends the
  resulting text to the given string buffer.  The type of monetary value argument can be
  any one of any of the following classes: {@link Coin},
  {@link Integer}, {@link Long}, {@link BigInteger},
  {@link BigDecimal}.  Numeric types that can represent only an integer are interpreted
  as that number of satoshis.  The value of a {@link BigDecimal} is interpreted as that
  number of bitcoins, rounded to the nearest satoshi as necessary.
  
  @return the {@link StringBuffer} passed in as {@code toAppendTo}