Datagrid row does not retain the color assigned by a trigger

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C#

DataGrid

Hello to all the friends of the forum: I have the following code in a purchase datagrid, where the trigger is activated if the purchase date field is blank, color the corresponding row with an alert color.

<Datagrid.RowStyle>
	<Style.Triggers>
		<DataTrigger Binding="{Binding BuyDate}" Value="">
			<Setter Property="Background" Value="Orange"/>
		</Datatrigger>
	</style.Triggers>
</Datagrid.RowStyle>

The last row of the datagrid always has the date blank, but it does not color it, the other rows that meet the condition do color it. But if I am reviewing the rows from top to bottom of the datagrid, the color of the rows where the trigger is fulfilled, they lose their color, that is, how the trigger did not work and the color of the last row is also activated. I don't understand why this is happening, am I missing some detail?

Very grateful for the help.
(Sorry for my bad english)

What I have tried:

I'm new to WPF and can't find the proper documentation.