Conversion from type 'DBNull' to type 'String' is not valid

Question

i am receiving this problem

Conversion from type \'DBNull\' to type \'String\' is not valid.

Line 501: hfSupEmail.

Answer 1

You should handle it at DB query level itself.

instead of "select name from student", use "select IsNull(name,'') as name from student"

In this way, DB will handle your NULL value.

Answer 2

To handle it from code, here is a small extension method

Imports Microsoft.VisualBasic
Imports System.Runtime.CompilerServices

Public Module HTMLExtensionMethods
    <Extension()> _
    Public Function DefaultIfDBNull(Of T)(ByVal obj As Object) As T
        Return If(Convert.IsDBNull(obj), CType(Nothing, T), CType(obj, T))
    End Function
End Module

Call it like this.

hfSupEmail.Value = dt.Rows(0)("SupEmail").DefaultIfDBNull(Of String)()