"Can't figure out which ctor to call." error with CosmosDB trigger

I'm trying to run a new Function locally. It uses the CosmosDB trigger. Building works fine, but when trying to run with `func host start`, I get this error: **The 'companiesWrite' function is in error: Unable to configure binding 'cosmosDBTrigger1' of type 'cosmosDBTrigger'. This may indicate invalid function.json properties. Can't figure out which ctor to call.**

I see a similar issue here: https://github.com/Azure/Azure-Functions/issues/277. The problem was a misnamed configuration property. But I checked all of mine against both the TypeScript def and the online documentation.

My code:

```typescript
import { app, InvocationContext } from "@azure/functions";

export async function companiesWrite(documents: any[], context: InvocationContext): Promise {
context.log(`Cosmos DB function processed ${documents.length} documents`);
}

app.cosmosDB('companiesWrite', {
connectionStringSetting: 'devworksafetyindex_DOCUMENTDB',
databaseName: 'wsi',
collectionName: 'companies',
createLeaseCollectionIfNotExists: true,
maxItemsPerInvocation: 40,
handler: companiesWrite
});
```

My host.json:

```json
{
"version": "2.0",
"logging": {
"applicationInsights": {
"samplingSettings": {
"isEnabled": true,
"excludedTypes": "Request"
}
}
},
"extensionBundle": {
"id": "Microsoft.Azure.Functions.ExtensionBundle",
"version": "[4.*, 5.0.0)"
}
}
```

I tried adding an HttpTrigger Function, and this worked fine. So it appears to be something specific to my CosmosDB trigger.

Thanks!