Meaning of is_required property in Handlebars template

[MaxiPigna]

I implemented a simple (Auto) Function Calling kernel.

var yamlPrompt = EmbeddedResource.Read("SomePrompt.yml");
var function = kernel.CreateFunctionFromPromptYaml(yamlPrompt, new HandlebarsPromptTemplateFactory());
var args = new KernelArguments(new OpenAIPromptExecutionSettings()
{
    ToolCallBehavior = ToolCallBehavior.AutoInvokeKernelFunctions,
})
{
    { "history", chatHistory }
};


var chatResponse = await kernel.InvokeAsync(function, args, cancellationToken);

with this Yaml prompt

name: SomePrompt
template: |
  Reply to user question.
  Search on {{knowledgeType}} knowledge
  Conversation:
  {{#each history}}
    <message role="{{role}}">{{content}}</message>
  {{/each}}
template_format: handlebars
description: A function that replies to user questions.
input_variables:
  - name: history
    description: conversation history
    is_required: true
  - name: knowledgeType
    description: type of knowledge that could be internal or external
    is_required: true
output_variable:
  description: Answer to question of the user
execution_settings:
  default:
    temperature: 0.1

Considering that knowledgeType is just an example, since is_required is true and I didn't provide the value in the kernel arguments, what is the expected behavior? Because, now it simply ignores it, so I don't understand what is the difference between is_required true and false. Thanks.

[matthewbolanos]

Is_required is information that is passed to the LLM to let it know that the input is required if it tries to use automatic function calling. You're right that we currently throwing an error. This may be a bug, so I'm going to create an issue for this.