KeyVaultReferencesManager throws an error when provided a null config item

When KeyVaultReferencesManager attempts to match config items with the Key Vault Reference format it can result in a cryptic error being thrown Key Vault Reference format invalid:

The following is an example from a newly created empty function app

local.settings.json

{
  "IsEncrypted": false,
  "Values": {
    "AzureWebJobsStorage": "UseDevelopmentStorage=true",
    "FUNCTIONS_WORKER_RUNTIME": "dotnet",
    "test": null
  }
}

On Debug

Azure Functions Core Tools
Core Tools Version:       3.0.4378 Commit hash: N/A  (64-bit)
Function Runtime Version: 3.4.2.0

[2022-03-17T01:43:06.010Z] Found C:\***\NullValueFunction\NullValueFunction.csproj. Using for user secrets file configuration.
Key Vault Reference format invalid:
Press any key to continue....

[k-krupka]

Just encountered this as well. For me the workaround was to remove all properties which are initialized with null values in appsettings.json, like this line: When i removed it, it’s all good and at least the function starts,

[j0hnth0m]

This should have been rolled back for both v4 and v3. The rolled back versions for Core Tools are 4.0.3971 and 3.0.3904.

Try deleting these folders and restarting VS to force it to update:

For v3:

C:\Users\ <user name> \AppData\Local\AzureFunctionsTools\Tags\v3 C:\Users\ <user name> \AppData\Local\AzureFunctionsTools\Releases\3.32.0

For v4:

C:\Users\ <user name> \AppData\Local\AzureFunctionsTools\Tags\v4 C:\Users\ <user name> \AppData\Local\AzureFunctionsTools\Releases\4.11.0

Thanks, that cleared up the problem. Both V3 and V4 function runtimes are working again.