Dispatcher Workspace : "Assignment Group" value from URL isn't applied until selected from dropdown

[GurshrutisS]

Hi everyone , 

In dispatcher workspace i am try to prefill assignment group via URL  (I have created a optional parameter). The value appears in input but does not get applied .For applying it , I manually have to select it from dropdown and apply.
I want assignment group needs to be prefilled (and applied) once value is present in URL .  

How can i make this possible ?

Thanks