Could Not Retrieve Information for Folder Error is Thrown on Loading the Web Designer

Environment

Product	Progress® Telerik® Reporting
Project Type	Web Application

Description

On loading the Web Report Designer, an error is thrown in the bottom right corner, and also in the browser's console

Error Message

Could not retrieve information for folder. Error: An error has occurred.

Possible Cause

The ReportDesignerControllerBase includes the following method:

public override IActionResult GetFolderModel([FromQuery] string uri)

The problem is that parameters on actions are treated as required if they do not have the nullable? annotation.

Suggested Workarounds

Configure the Nullable setting of the Project to warnings

Open the .csproj file of your project and add the following setting:

<Nullable>warnings</Nullable>

Override ReportDesignerControllerBase Actions To Include Nullable? Annotations

The methods of the ReportDesignerControllerBase class are virtual and thus, they can be overriden. In this case, the following method can be overriden to fix the error:

public override IActionResult GetFolderModel([FromQuery] string? uri)
{
    return base.GetFolderModel(uri);
}