Add error handling for missing xslt configuration.

src/main/kotlin/KafkaTopology.kt

@@ -20,12 +20,14 @@ package org.memobase
 
 import ch.memobase.kafka.utils.ConfigJoiner
 import ch.memobase.kafka.utils.models.ImportService
+import ch.memobase.kafka.utils.models.JoinedValues
 import com.beust.klaxon.Klaxon
 import org.apache.kafka.common.serialization.Serdes
 import org.apache.kafka.streams.KeyValue
 import org.apache.kafka.streams.StreamsBuilder
 import org.apache.kafka.streams.Topology
 import org.apache.kafka.streams.kstream.KStream
+import org.apache.kafka.streams.kstream.Predicate
 import org.apache.logging.log4j.LogManager
 import org.memobase.models.*
 import org.memobase.settings.SettingsLoader
@@ -67,10 +69,26 @@ class KafkaTopology(private val settings: SettingsLoader) {
 
         val joinedStream = configJoiner.join(dataStream, configStream)
 
-        val saxHandlerStream = joinedStream
+        val configNullBranch = joinedStream
+            .branch(
+                Predicate { _, value -> value.right == null },
+                Predicate { _, _ -> true }
+            )
+
+        configNullBranch[0]
+            .transformValues(HeaderExtractionTransformSupplier<JoinedValues<Message, ByteArray>>())
+            .mapValues { key, value ->
+                Report(
+                    key,
+                    ReportStatus.failure,
+                    "Could not find a matching xslt configuration for record set ${value.second.recordSetId}."
+                )
+            }
+
+        val saxHandlerStream = configNullBranch[1]
             .mapValues { value ->
-                log.debug("Combine joined inputs.")
-                Input(value.left, value.right) }
+                Input(value.left, value.right)
+            }
             .transformValues(HeaderExtractionTransformSupplier<Input>())
             .mapValues { value ->
                 Content(