Error : Conversion from type 'DBNull' to type 'Integer' is not valid.

Count = objCmd.ExecuteScalar()

         Try
         Count = objCmd.ExecuteScalar()
        Catch ex As Exception
        Count = 0
        End Try

Imports System.Data.SqlClient

Public Class Manage_RawMaterial_New
    Inherits System.Web.UI.Page

    Dim objConn As SqlConnection
    Dim objCmd As SqlCommand
    Dim strConnString, strSQL As String

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

    End Sub

    Public Sub ConnectDB()

        strConnString = ConfigurationManager.ConnectionStrings("con").ConnectionString
        objConn = New SqlConnection(strConnString)

    End Sub

    Private Sub AddAutoID()
        Try
            Dim intNum As String = Nothing
            Dim Count As Integer

            ConnectDB()

            strSQL = "SELECT ISNULL(MAX(RIGHT(RM_ID,4)),0) AS RM_ID FROM RawMaterial_New"
            objCmd = New SqlCommand(strSQL, objConn)

            objConn.Open()
            Count = objCmd.ExecuteScalar()
            objConn.Close()

            Dim iMAX As Integer = IIf(Count <= 0, 1, Count + 1)
            If iMAX < 10000 Then
                strSQL = "INSERT INTO RawMaterial_New (RM_ID) VALUES ('" & iMAX.ToString("RM0000") & "')"
                objCmd = New SqlCommand(strSQL, objConn)

                objConn.Open()
                objCmd.ExecuteNonQuery()
                objConn.Close()

                MsgBox("บันทึกสำเร็จ")
            Else
                MsgBox("ข้อมูลเต็ม")
            End If
        Catch ex As Exception
            Response.Write("Error : " + ex.Message)
        End Try

    End Sub

    Protected Sub btnRM_Add_Click(sender As Object, e As EventArgs) Handles btnRM_Add.Click

        AddAutoID()

    End Sub

End Class