Is this a bug or designed this way?

I have a scenario with 2 col which are dependent on each other (i.e: selecting 1 will populate the 2nd one). The value of the 2nd dropdown is the one that is passed to the server and this value is not mandatory.

So If I select dropdown 1 & dont select anything in dropdown 2(automatically goes to please select).. when I submit my form, an empty value is sent to the server.