CosmosDB Outputbinding does not work for multiple documents

We have a simple function which is triggered by event hub and simply forwards messages to cosmosDB using the cosmosDB output binding.
It works well if we receive and forward one message.
However it does not work when we receive and forward a list of messages using Cardinality.many.
Example:
```
public void run(
@EventHubTrigger(
name = "ConsumeDeviceMessages2",
eventHubName = "@eventhub.name@",
connection = "@iothub.connection@",
consumerGroup = CONSUMER_GROUP,
cardinality = Cardinality.MANY)
List messages,

@CosmosDBOutput(
name = "outputDocument",
databaseName = "@cosmosdb.name@",
collectionName = "@cosmosdb.collection.name@",
connectionStringSetting = "@cosmosdb.connection.appsetting@")
OutputBinding> outputDocument,

final ExecutionContext context) {
outputDocument.setValue(messages);
}
```
If this is triggered an error occurs:

`[Error] Executed 'Functions.SaveIotDeviceMessages' (Failed, Id=a845d74b-861a-40e7-a6f2-f5b7032b2cf2)Value cannot be null.Parameter name: document`

Configuration seems pretty basic and works on another function where we forward multiple messages to a queue instead.

Any idea why it is not working for cosmosDB? The documentation states its working for .NET and Javascript, no information about Java though.

Thanks and regards.

Beginnen Sie damit, die Java-Funktion mit EventHubTrigger Cardinality.MANY und CosmosDBOutput unter Verwendung von OutputBinding> zu reproduzieren. Verfolgen Sie, wie das Java-CosmosDB-Output-Binding outputDocument.setValue(messages) verarbeitet, und vergleichen Sie sein Verhalten mit der dokumentierten Unterstützung in .NET und JavaScript. Als abgeschlossen gilt die Ermittlung, ob mehrere Dokumente in Java unterstützt werden, sowie die Dokumentation oder Korrektur des resultierenden Verhaltens.

Vom Indexierungsmodell aus dem Issue-Text verfasst.