null value in Eval

 i have a listview with sqlDataSource in my webpage.
i would like to display in one of the labels in the itemtemplate just part of the text so i am using :
<%# Eval("PText").ToString().Substring(0,40) %> the problem is that i gt exception when the PText value return from the database is null, what should i do ?
is there any way to get over it without checking the value in the databound event ? what is the best way ?
Thanks

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