code: public static BigInteger convertVarNumberToBigInteger(byte[] rawData) {
  		BigInteger result=BigInteger.ZERO;
  		if (rawData!=null) {
  			if (rawData.length>0) {
  				result = new BigInteger(1,rawData); // we know it is always positive
  			}
  		}
  		return result;
  }
docs: *
  Converts a variable size number (e.g. byte,short,int,long) in a RLPElement to long
  
  @param rawData byte array containing variable number
  @return number as long or null if not a correct number