code: public IssuingDistributionPointExtension
          getIssuingDistributionPointExtension() throws IOException {
  
          Object obj = getExtension(PKIXExtensions.IssuingDistributionPoint_Id);
          return (IssuingDistributionPointExtension) obj;
      }
docs: return the IssuingDistributionPointExtension, if any.
  
  @returns IssuingDistributionPointExtension or null
  (if no such extension)
  @throws IOException on error