code: public static byte[] encodeInteger(BigInteger bigInt) {
          if (bigInt == null) {
              throw new NullPointerException("encodeInteger called with null parameter");
          }
          return encodeBase64(toIntegerBytes(bigInt), false);
      }
docs: Encodes to a byte64-encoded integer according to crypto standards such as W3C's XML-Signature
  
  @param bigInt a BigInteger
  @return A byte array containing base64 character data
  @throws NullPointerException if null is passed in
  @since 1.4