code: @Override
  	public BigInteger getBigInteger(final String key, final BigInteger defaultValue) {
  		try {
  			String value = get(key);
  
  			if (value == null) {
  				return defaultValue;
  			}
  
  			return new BigInteger(value);
  		} catch (NumberFormatException ex) {
  			throw new ConversionException(ex);
  		}
  	}
docs: {@inheritDoc}