Fix exception when passing model: null to the api/pdf endpoint

[Copilot]

The API was throwing an InvalidOperationException when a user passed model: null in the JSON request body to the /api/pdf endpoint. This occurred because the JsonDocumentExtensions.ConvertElement method only handled JsonValueKind.Object and JsonValueKind.Array types, but not JsonValueKind.Null at the root level.

Issue

When sending a request like this:

{
  "template": "My Template!",
  "model": null,
  "options": {
    "pageSize": "A4",
    "orientation": "Portrait", 
    "margin": null
  },
  "templateEngine": "razor",
  "fileName": null
}

The following exception was thrown:

System.InvalidOperationException: Unsupported JSON ValueKind: Null
   at PdfSmith.BusinessLayer.Extensions.JsonDocumentExtensions.ConvertElement(JsonElement element, TimeZoneInfo timeZoneInfo)

Solution

Modified the ConvertElement method to delegate non-Object/Array cases to the existing ConvertValue method, which already properly handles all JsonValueKind values including Null. This is a minimal change that reuses existing logic and maintains backward compatibility.

Changes

• Updated ConvertElement to return object? instead of throwing for unsupported value kinds
• Updated ToExpandoObject return type to object? to properly reflect nullable results
• Added delegation to ConvertValue for handling all non-Object/Array cases

The fix ensures that model: null is properly handled by returning null instead of throwing an exception, while preserving all existing functionality for object and array models.

Fixes #28.

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[Copilot]

Pull Request Overview

This pull request fixes an exception that occurred when passing model: null to the /api/pdf endpoint. The main issue was that the JSON deserialization logic in JsonDocumentExtensions.ConvertElement only handled Object and Array types, throwing an InvalidOperationException for null values.

Key changes made:

• Modified ConvertElement method to delegate non-Object/Array cases to the existing ConvertValue method instead of throwing exceptions
• Updated template engine interfaces and implementations to accept nullable model parameters
• Simplified PDF generation logic to handle null models consistently

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
JsonDocumentExtensions.cs	Fixed the core issue by delegating null/primitive value handling to existing ConvertValue method
ITemplateEngine.cs	Updated interface to accept nullable model parameter
ScribanTemplateEngine.cs	Updated implementation to handle nullable models and fixed constant name
RazorTemplateEngine.cs	Updated to accept nullable models and removed extra whitespace
HandlebarsTemplateEngine.cs	Updated to accept nullable models
PdfService.cs	Simplified logic to use null-conditional operator for model conversion

Comments suppressed due to low confidence (1)

src/PdfSmith.BusinessLayer/Templating/ScribanTemplateEngine.cs:13

• The constant name change from 'date_time_zone' to 'datetime_withzone' appears unrelated to the null model fix. This naming change should be separated into its own PR or better justified in the current context.

    private const string DateTimeZonePlaceholder = "datetime_withzone";

[Copilot]

[nitpick] The logic has been simplified but the control flow could be clearer. Consider handling the null model case explicitly rather than relying on the null-conditional operator, especially since the original code had separate paths for null vs non-null models.

Suggested change

	var model = request.Model?.ToExpandoObject(timeZoneInfo);
	object? model;
	if (request.Model is null)
	{
	model = null;
	}
	else
	{
	model = request.Model.ToExpandoObject(timeZoneInfo);
	}