Testing Split elements

[tester_V]

I do not have a problem splitting.
I need to replace the fourth element in a split if the element does not exist.
Here is a line to split:

   Motherboard:   Ao11   Build-211   DT 2021 SN-0123A456

if the line has nothing after the word "Motherboard:"

   Motherboard:  

I want to print something like "not there" or "empty" or "No Serial Num"
I thought I could split the line and test elements if they are ==0 or not.
That is why I'm testing element 4 if it is empty.

    mb=re.split(r" {2,}", rn_l)
    if not mb[4] :
       mb[4] ="No Serial Num"
    else :
        print (f" Motherboard Serial number   -->> {mb[4]}")