Getting a "Conversion from type 'DBNull' to type 'String' is not valid" error.

Isn't this the correct way to check for NULLS if the value is coming from a Database? I'm getting the  "Conversion from type 'DBNull' to type 'String' is not valid" error on the indicated line. The variable clsDE.capacity is defined as a "String".

    Public Function GetDetailsEquipmentRecord(ByVal iEquipment_ID As Integer, ByVal clsDE As CalTableClasses.CalibrationClasses.DETAILS_Equipment, ByVal EH As ErrorHandling.ErrorHandler)
        Try
            DL.GetDetailsEquipmentRecord(iEquipment_ID, EH)

            If EH.Success Then
                If EH.DataSet.Tables(0).Rows.Count = 1 Then
                    Dim row2 As DataRow = EH.DataSet.Tables(0).Rows(0)
                    clsDE.capacity = If(DBNull.Value.ToString.Equals(row2("Capacity")), "", row2("Capacity"))  '----------> Throwing exception
                End If
            End If

        Catch ex As Exception
            EH.ErrorMessage = "CalBusiness/GetDetailsEquipmentRecord() - " & ex.Message & "~E"
        End Try

        Return EH
    End Function

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