Azure Functions Python blobTrigger How do I fix “Microsoft.Azure.WebJobs.Extensions.Storage: Object reference not set to an instance of an object.”?

Question

Update below with more detailed debug output

I have successfully run Azure Functions using the local dev host in the past.

I have not been able to get the blobTrigger working recently. I have taken the following steps:

func init NewWave
cd NewWave
func new # -> select httpTrigger called HttpTrigger in language python
func new # -> select blobTrigger called BlobTrigger in language python
func host start

host.json contains:

{
    "version": "2.0",
    "extensionBundle": {
        "id": "Microsoft.Azure.Functions.ExtensionBundle",
        "version": "[1.*, 2.0.0)"
    }
}

local.settings.json contains:

{
  "IsEncrypted": false,
  "Values": {
    "FUNCTIONS_WORKER_RUNTIME": "python",
    "AzureWebJobsStorage": "{AzureWebJobsStorage}"
  }
}

AzureWebJobsStorage is a connection string set via an environment variable.

BlobTrigger/function.json contains:

{
  "scriptFile": "__init__.py",
  "bindings": [
    {
      "name": "myblob",
      "type": "blobTrigger",
      "direction": "in",
      "path": "samples-workitems/{name}",
      "connection": ""
    }
  ]
}

__init__.py contains:

import logging

import azure.functions as func


def main(myblob: func.InputStream):
    logging.info(f"Python blob trigger function processed blob \n"
                 f"Name: {myblob.name}\n"
                 f"Blob Size: {myblob.length} bytes")

HttpTrigger loads but BlobTrigger does not. The output is:

Azure Functions Core Tools (2.7.1373 Commit hash: cd9bfca26f9c7fe06ce245f5bf69bc6486a685dd)
Function Runtime Version: 2.0.12507.0
Warning: 'connection' property in '~/NewWave/BlobTrigger/function.json' is empty.
Skipping 'AzureWebJobsStorage' from local settings as it's already defined in current environment variables.
[...]
[6/24/19 12:45:28 PM] Starting JobHost
[...]
[6/24/19 12:45:28 PM] Generating 2 job function(s)
[6/24/19 12:45:28 PM] Found the following functions:
[6/24/19 12:45:28 PM] Host.Functions.HttpTrigger
[6/24/19 12:45:28 PM] Host.Functions.BlobTrigger
[6/24/19 12:45:28 PM]
[6/24/19 12:45:28 PM] Host initialized (280ms)

Http Functions:

    HttpTrigger: [GET,POST] http://localhost:7071/api/HttpTrigger

[6/24/19 12:45:28 PM] A host error has occurred
[6/24/19 12:45:28 PM] Microsoft.Azure.WebJobs.Extensions.Storage: Object reference not set to an instance of an object.
[6/24/19 12:45:28 PM] Stopping JobHost

What is causing this error and how can I resolve it?

If any further settings, logs etc. are required please advise in the comments below and I will update.

Thanks

OS: macOS High Sierra 10.13.6

Python version:

Python 3.6.8 |Anaconda, Inc.| (default, Dec 29 2018, 19:04:46) [GCC 4.2.1 Compatible Clang 4.0.1 (tags/RELEASE_401/final)] on darwin Type "help", "copyright", "credits" or "license" for more information.

pip freeze:

azure==4.0.0 azure-applicationinsights==0.1.0 azure-batch==4.1.3 azure-cognitiveservices-vision-customvision==1.0.0 azure-common==1.1.20 azure-cosmosdb-nspkg==2.0.2 azure-cosmosdb-table==1.0.5 azure-datalake-store==0.0.45 azure-eventgrid==1.2.0 azure-functions==1.0.0b4 azure-functions-worker==1.0.0b8 azure-graphrbac==0.40.0 azure-keyvault==1.1.0 azure-loganalytics==0.1.0 azure-mgmt==4.0.0 azure-mgmt-advisor==1.0.1 azure-mgmt-applicationinsights==0.1.1 azure-mgmt-authorization==0.50.0 azure-mgmt-batch==5.0.1 azure-mgmt-batchai==2.0.0 azure-mgmt-billing==0.2.0 azure-mgmt-cdn==3.1.0 azure-mgmt-cognitiveservices==3.0.0 azure-mgmt-commerce==1.0.1 azure-mgmt-compute==4.6.2 azure-mgmt-consumption==2.0.0 azure-mgmt-containerinstance==1.4.1 azure-mgmt-containerregistry==2.8.0 azure-mgmt-containerservice==4.4.0 azure-mgmt-cosmosdb==0.4.1 azure-mgmt-datafactory==0.6.0 azure-mgmt-datalake-analytics==0.6.0 azure-mgmt-datalake-nspkg==3.0.1 azure-mgmt-datalake-store==0.5.0 azure-mgmt-datamigration==1 .0.0 azure-mgmt-devspaces==0.1.0 azure-mgmt-devtestlabs==2.2.0 azure-mgmt-dns==2.1.0 azure-mgmt-eventgrid==1.0.0 azure-mgmt-eventhub==2.6.0 azure-mgmt-hanaonazure==0.1.1 azure-mgmt-iotcentral==0.1.0 azure-mgmt-iothub==0.5.0 azure-mgmt-iothubprovisioningservices==0.2.0 azure-mgmt-keyvault==1.1.0 azure-mgmt-loganalytics==0.2.0 azure-mgmt-logic==3.0.0 azure-mgmt-machinelearningcompute==0.4.1 azure-mgmt-managementgroups==0.1.0 azure-mgmt-managementpartner==0.1.0 azure-mgmt-maps==0.1.0 azure-mgmt-marketplaceordering==0.1.0 azure-mgmt-media==1.0.0 azure-mgmt-monitor==0.5.2 azure-mgmt-msi==0.2.0 azure-mgmt-network==2.7.0 azure-mgmt-notificationhubs==2.1.0 azure-mgmt-nspkg==3.0.2 azure-mgmt-policyinsights==0.1.0 azure-mgmt-powerbiembedded==2.0.0 azure-mgmt-rdbms==1.8.0 azure-mgmt-recoveryservices==0.3.0 azure-mgmt-recoveryservicesbackup==0.3.0 azure-mgmt-redis==5.0.0 azure-mgmt-relay==0.1.0 azure-mgmt-reservations==0.2.1 azure-mgmt-resource==2.1.0 azure-mgmt-scheduler==2.0.0 azure-mgmt-search= =2.0.0 azure-mgmt-servicebus==0.5.3 azure-mgmt-servicefabric==0.2.0 azure-mgmt-signalr==0.1.1 azure-mgmt-sql==0.9.1 azure-mgmt-storage==2.0.0 azure-mgmt-subscription==0.2.0 azure-mgmt-trafficmanager==0.50.0 azure-mgmt-web==0.35.0 azure-nspkg==3.0.2 azure-servicebus==0.21.1 azure-servicefabric==6.3.0.0 azure-servicemanagement-legacy==0.20.6 azure-storage==0.36.0 azure-storage-blob==2.0.1 azure-storage-common==2.0.0 azure-storage-file==1.4.0 azure-storage-queue==1.4.0 msrestazure==0.6.0

Update

I've found some more detailed log files (note that I am on macOS) thus:

2019-06-24T11:14:42.213 [Error] A host error has occurred
System.NullReferenceException : Object reference not set to an instance of an object.
   at Microsoft.Azure.WebJobs.Host.Blobs.Listeners.CloudBlobClientComparer.GetHashCode(CloudBlobClient obj) at C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Extensions.Storage\Blobs\Listeners\CloudBlobClientComparer.cs : 34
   at System.Collections.Generic.Dictionary`2.TryInsert(TKey key,TValue value,InsertionBehavior behavior)
   at System.Collections.Generic.Dictionary`2.Add(TKey key,TValue value)
   at async Microsoft.Azure.WebJobs.Host.Blobs.Listeners.PollLogsStrategy.RegisterAsync(CloudBlobContainer container,ITriggerExecutor`1 triggerExecutor,CancellationToken cancellationToken) at C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Extensions.Storage\Blobs\Listeners\PollLogsStrategy.cs : 74
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.Azure.WebJobs.Host.Blobs.Listeners.ScanBlobScanLogHybridPollingStrategy.RegisterAsync(CloudBlobContainer container,ITriggerExecutor`1 triggerExecutor,CancellationToken cancellationToken) at C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Extensions.Storage\Blobs\Listeners\ScanBlobScanLogHybridPollingStrategy.cs : 61
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.Azure.WebJobs.Host.Blobs.Listeners.BlobListenerFactory.RegisterWithSharedBlobListenerAsync(String hostId,SharedBlobListener sharedBlobListener,CloudBlobClient blobClient,CloudQueue hostBlobTriggerQueue,IMessageEnqueuedWatcher messageEnqueuedWatcher,CancellationToken cancellationToken) at C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Extensions.Storage\Blobs\Listeners\BlobListenerFactory.cs : 155
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.Azure.WebJobs.Host.Blobs.Listeners.BlobListenerFactory.CreateAsync(CancellationToken cancellationToken) at C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Extensions.Storage\Blobs\Listeners\BlobListenerFactory.cs : 93
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.Azure.WebJobs.Host.Indexers.FunctionIndexer.ListenerFactory.CreateAsync(CancellationToken cancellationToken) at C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Indexers\FunctionIndexer.cs : 426
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.Azure.WebJobs.Host.Listeners.HostListenerFactory.CreateAsync(CancellationToken cancellationToken) at C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Listeners\HostListenerFactory.cs : 62
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.Azure.WebJobs.Host.Listeners.ListenerFactoryListener.StartAsyncCore(CancellationToken cancellationToken) at C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Listeners\ListenerFactoryListener.cs : 45
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.Azure.WebJobs.Host.Listeners.ShutdownListener.StartAsync(CancellationToken cancellationToken) at C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Listeners\ShutdownListener.cs : 29
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.Azure.WebJobs.JobHost.StartAsyncCore(CancellationToken cancellationToken) at C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\JobHost.cs : 101
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.Azure.WebJobs.Script.ScriptHost.StartAsyncCore(CancellationToken cancellationToken) at C:\azure-webjobs-sdk-script\src\WebJobs.Script\Host\ScriptHost.cs : 241
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.Extensions.Hosting.Internal.Host.StartAsync(CancellationToken cancellationToken)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.Azure.WebJobs.Script.WebHost.WebJobsScriptHostService.StartHostAsync(CancellationToken cancellationToken,Int32 attemptCount,JobHostStartupMode startupMode) at C:\azure-webjobs-sdk-script\src\WebJobs.Script.WebHost\WebJobsScriptHostService.cs : 163

Answer 1

I would suggest you to add a value in " connection " which is empty in your setting

{
    "scriptFile": "__init__.py",
    "disabled": false,
    "bindings": [
        {
            "name": "myblob",
            "type": "blobTrigger",
            "direction": "in",
            "path": "samples-workitems/{name}",
            "connection":"MyStorageAccountAppSetting"
        }
    ]
}

here is my local.settings.json

{
  "IsEncrypted": false,
  "Values": {
    "AzureWebJobsStorage": "",
    "FUNCTIONS_WORKER_RUNTIME": "python",
    "mohitsa_STORAGE": ""
  }
}

Hope it helps.

Answer 2

By trial and error - and a completely misleading error message...

The answer is simply to set the environment variable AzureWebJobsStorage to the Storage account's master Access key Connection string, which looks something like this:

DefaultEndpointsProtocol=https;AccountName=<account name>;AccountKey=<account key>;EndpointSuffix=core.windows.net

rather than the SAS Connection string created via az storage account generate-sas