) -> script::Builder {
    builder = builder
      .push_opcode(opcodes::OP_FALSE)
      .push_opcode(opcodes::all::OP_IF)
      .push_slice(envelope::PROTOCOL_ID);

    if let Some(content_type) = self.content_type.clone() {
      builder = builder
        .push_slice(envelope::CONTENT_TYPE_TAG)
        .push_slice(PushBytesBuf::try_from(content_type).unwrap());
    }

    if let Some(content_encoding) = self.content_encoding.clone() {
      builder = builder
        .push_slice(envelope::CONTENT_ENCODING_TAG)
        .push_slice(PushBytesBuf::try_from(content_encoding).unwrap());
    }

    if let Some(protocol) = self.metaprotocol.clone() {
      builder = builder
        .push_slice(envelope::METAPROTOCOL_TAG)
        .push_slice(PushBytesBuf::try_from(protocol).unwrap());
    }

    if let Some(parent) = self.parent.clone() {
      builder = builder
        .push_slice(envelope::PARENT_TAG)
        .push_slice(PushBytesBuf::try_from(parent).unwrap());
    }

    if let Some(pointer) = self.pointer.clone() {