code: public Integer getReasonCode() throws IOException {
          Object obj = getExtension(PKIXExtensions.ReasonCode_Id);
          if (obj == null)
              return null;
          CRLReasonCodeExtension reasonCode = (CRLReasonCodeExtension)obj;
          return reasonCode.get(CRLReasonCodeExtension.REASON);
      }
docs: get Reason Code from CRL entry.
  
  @returns Integer or null, if no such extension
  @throws IOException on error