There is no error message in response while failing to create function app

Symptom:
After tested, I found that there is no error message in response, no error message in ServiceError and no StatusCode since they all are nil while failing to create function app. It should return the error message in response.

Rest api call:
```
PUT https://management.azure.com/subscriptions/xx-xx-xx-xx/resourceGroups/acctestRG-xxx/providers/Microsoft.Web/sites/acctest-xxx-func

{
"kind": "functionapp",
"location": "westus2",
"properties": {
"enabled": true,
"serverFarmId": "/subscriptions/xx-xx-xx-xx/resourceGroups/acctestRG-xxx/providers/Microsoft.Web/serverfarms/acctestASP-xxx",
"siteConfig": {
"linuxFxVersion": "",
"appSettings": [
{
"name": "AzureWebJobsStorage",
"value": "DefaultEndpointsProtocol=https;AccountName=xxxxx;AccountKey=xxxxx;EndpointSuffix=xxxx"
},
{
"name": "FUNCTIONS_EXTENSION_VERSION",
"value": "~1"
},
{
"name": "AzureWebJobsDashboard",
"value": "DefaultEndpointsProtocol=https;AccountName=xxxxxx;AccountKey=xxxxxx;EndpointSuffix=xxxxx"
}
],
"use32BitWorkerProcess": true,
"webSocketsEnabled": false,
"alwaysOn": false,
"cors": {
"allowedOrigins": [
"*"
],
"supportCredentials": true
},
"ipSecurityRestrictions": [],
"http20Enabled": false,
"ftpsState": "Disabled",
"preWarmedInstanceCount": 0
},
"clientAffinityEnabled": false,
"dailyMemoryTimeQuota": 0,
"httpsOnly": false
},
"tags": {}
}
```

Result:

Locate the Azure specification for the shown PUT operation that creates a function app, then inspect how failure responses are defined for that operation. Confirm the expected error payload and status code from the service behavior, and verify that the specification represents them so failed requests expose an error message.

Written by the indexing model from the issue text.