If the Grid has no data, selecting null PageSize throws:

Error: System.ArgumentException: Page Size cannot be less than one (Parameter 'PageSize') 

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ADMIN EDIT

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A possible workaround for the time being will be to use some conditional CSS to disable the PageSize dropdown while there is no data in the Grid: https://blazorrepl.telerik.com/QcOpkTlb38EDFboT34.