Cast from type DBNull to type String is not valid

In vb.net using sql to escape this error "Cast from type DBNull to type String is not valid"
I use "ISNULL(E_ID,'') AS E_ID" in a sql statement
but this will not work when select data from an access database.
Is there a similiar command I can enter in vb.net to stop this error message when selecting from an access database.
Thanks
Regards
Gary
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