Object reference not set to an instance of an object

I am trying to input this rectangle as geometry into design space component “topopt plug-in” but it still give me this error

You’ll have to provide more details and possibly mention the developers of “topopt plug-in” in order to get some help! @Nehalnasser26

here is the gh and rhino files of what i am trying to do
typology optmization of simple beam with two support at the ends and central load in the middle of the beam .

example1.3dm (25.5 KB)
example1.gh (15.2 KB)