IS empty in vb.net to replace with a value if it is empty

Hi,
   I am inserting a text box value using Linq (Stored procedure)
in one like i would like to check for empty values of that text box value and as well as replace it with a value if its empty in that parameter place for SP in vb.net.
like we do in SQL .... ISNULL(something,0) etc.
Did not want to write the empty checks in two lines.
Please help me.