code: public DERObject toASN1Object()
      {
          ASN1EncodableVector v = new ASN1EncodableVector();
  
          v.add(base);
  
          if (minimum != null)
          {
              v.add(new DERTaggedObject(false, 0, minimum));
          }
  
          if (maximum != null)
          {
              v.add(new DERTaggedObject(false, 1, maximum));
          }
  
          return new DERSequence(v);
      }
docs: /*
  GeneralSubtree ::= SEQUENCE {
  base                    GeneralName,
  minimum         [0]     BaseDistance DEFAULT 0,
  maximum         [1]     BaseDistance OPTIONAL }