Check if image column is Null VB.NET - vb.net

Question

Good Day everyone. I need help with my code below.
Dim stream As New MemoryStream()
connect()
Dim command As New SqlCommand("SELECT image FROM tblHouseholdMembers WHERE id= '" & lvmem.FocusedItem.Text & "'", cn)
Dim image As Byte() = DirectCast(command.ExecuteScalar(), Byte()) --> 'Error message of null image
stream.Write(image, 0, image.Length)
cn.Close()
Dim bitmap As New Bitmap(stream)
pbProfilePic.Image = bitmap
I want to put a messagebox to identify if it's null before the error cast.

Answer 1

Instead of using the DirectCast method, use the TryCast and then check if the casting result is nothing:
Dim image As Byte() = TryCast(command.ExecuteScalar(), Byte())
if image isnot nothing then
stream.Write(image, 0, image.Length)
cn.Close()
Dim bitmap As New Bitmap(stream)
pbProfilePic.Image = bitmap
else
'Error message here
end if

Answer 2

The way to directly test if a field coming back from a database is null is:
if ValueFromDb is System.DbNull.Value then
' whatever you want to do in that case
Something that really confused me when I was first learning VB is that a null value from a DB read is NOT equal to Nothing. It is not Nothing, it is System.DbNull.Value.
Most of my projects these days, I write a little function I call "denull" that says something like:
public shared function denull(value as object, defalt as object)
if value is system.dbnull.value then
return defalt
else
return value
end function
Then I wrap every value I read from the db in this function. This saves a lot of code.
for each row in mydataset.tables(0).rows
foo=denull(row("foo"),"")
bar=denull(row("bar"),0)
plugh=denull(row("plugh"),nothing)
... etc ...