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Add a KB on null reference exception from the GridRowCollection class #2006

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Add a KB on null reference exception from the GridRowCollection class #2006

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---
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title: Null Reference Expection from the GridRowCollection
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description: Fixing a Null Reference Exception Thrown from the GridRowCollection.
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type: troubleshooting
page_title: Null Reference Expection from the GridRowCollection
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slug: grid-kb-nullref-gridrowcollection
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position:
tags:
ticketid: 1643250, 1642910, 1604815, 1574971, 1577863, 1580684
res_type: kb
---

## Environment
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As the issue is version-related, you can add the affected versions to the table. In this case, they are "3.0.0 and later".

<table>
<tbody>
<tr>
<td>Product</td>
<td>Grid for Blazor</td>
</tr>
</tbody>
</table>


## Description

I upgraded the version of the Telerik UI from Blazor components from `<3.0.0` to `>3.0.0` and I get a `NullReferenceException` from the `GridRowCollection` class.
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## Error Message

>warning Error: System.NullReferenceException: Object reference not set to an instance of an object.
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If the message spans multiple rows, present the entire message as a code block (```bash error message ```). If it can also appear on a single line, enclose it in backticks and render it as inline code.

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Example for multiline error messages: https://docs.telerik.com/blazor-ui/knowledge-base/root-component-null-reference

You can skip the backticks.

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Example for multiline error messages: https://docs.telerik.com/blazor-ui/knowledge-base/root-component-null-reference

You can skip the backticks.

@dimodi Just because you can do it doesn't mean that you should. The Formatting article in the Style Guide clearly prescribes using monospace for the error messages. Using a note of type warning to present an error message is not allowed.

at Telerik.Blazor.Components.Grid.GridRowCollection`1.BuildRenderTree(RenderTreeBuilder __builder)

## Cause

The Telerik Grid for Blazor throws a NullReferenceException from the GridRowCollection class when both the `Data` paramater and `OnRead` event handler are defined:
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````CSHTML

<TelerikGrid Data="@DataCollection" OnRead="@OnReadHandler">
...
</TelerikGrid>
````
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## Solution

Remove either the `Data` parameter or the `OnRead` event handler.
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If the developer has used OnRead for some reason, it's unlikely they will go back to Data. Thus the primary recommendation can be phrased in a different way. For example, focus on the new way to use OnRead and link the relevant documentation here. The "See Also" links are less visible by definition.


## See Also

* [Changes in the OnRead Event in 3.0.0]({%slug changes-in-3-0-0%}#onread)
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* [Common OnRead Documentation]({%slug common-features-data-binding-onread%})
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* [Common How to Provide Data Documentation]({%slug common-features-data-binding-overview%})
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