Portal does not accept an empty value for string parameters

[Yvand]

When creating an environment from an ARM template using the DevTest Labs portal, I get error The value must not be empty if I pass an empty value for a string parameter.

This example allows to reproduce the issue:

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "incomingIPAllowedForRDP": {
      "type": "string",
      "defaultValue": "*",
      "minLength": 0,
      "metadata": {
        "description": "Specify which IP addresses are allowed to use RDP to connect to the VMs:<br>- If empty: Firewall denies all incoming RDP traffic from Internet.<br>- If '*' (default): Firewall accepts all incoming RDP traffic from Internet.<br>- If 'IPAddress': Firewall accepts incoming RDP traffic only from the specified 'IPAddress'."
      }
    }
  },
  "variables": {
  },
  "resources": [
  ],
  "outputs": {
  }
}

More info:

• Passing an empty string using https://portal.azure.com/#create/Microsoft.Template/ works fine
• Passing an empty string using New-AzResourceGroupDeployment works fine