[Templating] Support for fallback values in Adaptive Card templates

[LuisM000]

I have a question about setting default and fallback values in Adaptive Card templates. For example, I have this simple Adaptive Card:

{
  "type": "AdaptiveCard",
  "version": "1.4",
  "body": [
    {
      "type": "TextBlock",
      "text": "Example Adaptive Card"
    },
    {
      "type": "ActionSet",
      "actions": [
        {
          "type": "Action.Submit",
          "title": "Click Me",
          "enabled": "${isEnabled}"
        }
      ]
    }
  ]
}

I want the enabled property of the button to be true by default (without passing any value during the Expand process) but also have the ability to pass a value and modify it, in this case, set it to false.

I tried the following approaches but encountered issues:

1. Using inline data binding ($data): If I include data inline in the adaptive card, the values don’t get overwritten during the Expand process.
2. Using conditionals: I attempted to set a default value with conditionals, but they don’t work properly when no value is passed in the context.

Here’s the code I use for expansion:

AdaptiveCardTemplate transformer = new AdaptiveCardTemplate(jsonTemplate);
var context = new EvaluationContext
{
    Root = jsonData,
};

string cardJson = transformer.Expand(context);

Is there a way to define a default value (e.g., true for enabled) while still allowing it to be overridden during the Expand process?