code: public static boolean isCurrencyAvailable(String code, String... providers) {
          return Objects.nonNull(MONETARY_CURRENCIES_SINGLETON_SPI()) && MONETARY_CURRENCIES_SINGLETON_SPI().isCurrencyAvailable(code, providers);
      }
docs: Allows to check if a {@link CurrencyUnit} instance is defined, i.e.
  accessible from {@link Monetary#getCurrency(String, String...)}.
  
  @param code      the currency code, not {@code null}.
  @param providers the (optional) specification of providers to consider.
  @return {@code true} if {@link Monetary#getCurrency(String, java.lang.String...)}
  would return a result for the given code.