null
        } else {
            val testCoverages = model.stages.flatMap { it.functionalTests }
            val foundTestCoverage =
                testCoverages.firstOrNull {
                    it.testType == TestType.PLATFORM &&
                        it.os == testCoverage.os &&
                        it.arch == testCoverage.arch &&

        val peekedHeader =
          reader.peekHeader()
            ?: throw ProtocolException("expected a value at $reader")

        val choice =
          choices.firstOrNull { it.matches(peekedHeader) }
            ?: throw ProtocolException(
              "expected a matching choice but was $peekedHeader at $reader",
            )

        return choice to choice.fromDer(reader)