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Value cannot be null. (Parameter 'format')


Product UI for Blazor


I am trying to use a Wizard component in an application that has localization enabled but I am getting an error.

Error Message

Unhandled exception rendering component: Value cannot be null. (Parameter 'format') System.ArgumentNullException: Value cannot be null. (Parameter 'format') at System.String.FormatHelper(IFormatProvider provider, String format, ParamsArray args) at System.String.Format(String format, Object arg0, Object arg1) at Telerik.Blazor.Components.TelerikWizard.get_PagerMessage() at Telerik.Blazor.Components.TelerikWizard.BuildRenderTree(RenderTreeBuilder __builder) at Microsoft.AspNetCore.Components.Rendering.ComponentState.RenderIntoBatch(RenderBatchBuilder batchBuilder, RenderFragment renderFragment) at Microsoft.AspNetCore.Components.RenderTree.Renderer.RenderInExistingBatch(RenderQueueEntry renderQueueEntry) at Microsoft.AspNetCore.Components.RenderTree.Renderer.ProcessRenderQueue()

Cause\Possible Cause(s)

You may run across a similar error for other components as well. It occurs if a component is used in a localized application, but the .resx files are missing some keys for the corresponding component.

The app either needs to implement localization for the Telerik components correctly, or not implement a localization service at all. Partial localization is not possible. So, it is essential that the .resx files for the Telerik components are always up-to-date and contain all the necessary keys.


To solve the issue, make sure that:

You can find the latest localization files in two places:

  • In the /Resources/ folder of our demo site. The demo site is part of the UI for Blazor installation: /demos/TelerikBlazorDemos/Resources/ (maintained by Telerik)
  • In the telerik/blazor-ui-messages GitHub repository (maintained by the community)

In some cases, you might not get an error, but components could appear partially localized (some texts are missing). More details on that are available at Partially Localized Components, Missing Text, Not Translated Text.

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