A list containing NOBODY as one of its entities

Question

I have a sub-routing in my code where each patch is asked to pick its closest & farthest turtle based on certain conditions. I keep getting this error after a couple of ticks

OF expected input to be a turtle agentset or turtle but got NOBODY instead.
error while patch 0 30 running OF
  called by procedure UPDATE-SUPPORT
  called by procedure GO
  called by Button 'Go'

There are two other routines where a turtle dies or is born depending on a few other metrics that are measured. I am not able to debug the code but what i have figured so far is that it happens after a turtle dies or is born.

Below is the code based on which the closest & farthest turtles are assigned at each tick.

to update-support    
  ask patches [ 
    let old-total sum [my-old-size] of parties
    set f-party []
    set h-party []

    set party-list (sort parties)
    set voteshare-list n-values length(party-list) [ (([my-old-size] of party ? ) + 1 ) / ( old-total + 1 ) ] 
    set party-citizen-dist n-values length(party-list) [ ( distance party ? ) ^ 2 ]    
    set f-list n-values length(party-list) [ ( ( 1 / ( item ? voteshare-list ) ) * ( item ? party-citizen-dist ) ) ] 
    set f-index position (min f-list) f-list    
    set h-list n-values length(party-list) [ ( ( item ? voteshare-list ) * ( item ? party-citizen-dist ) ) ]
    set h-index position (max h-list) h-list

    set f ((-1) * (min f-list))
    set h max h-list

    set f-party lput item f-index party-list f-party 
    set h-party lput item h-index party-list h-party
    set closest-party first f-party
    set farthest-party first h-party
    ]

After a turtle dies, when I inspected the patch which was throwing the error, i found the word nobody as an element in the list. The error is highlighted to be in the Party ? section while creating the voteshare-list in the above code

When I inspected the patch throwing the error, Party-list which is the list with all the current parties sorted was showing this:

Party-list: [(party 0) nobody (party 2)]

and my f-party list just had [(nobody)]

Has anyone faced such a situation.?

Below is the death & birth routine:

to party-death
   ask parties [if (fitness < survival-threshold and count parties > 2)
       [  die
       ] update-support
]

to party-birth
  ifelse (endogenous-birth? = true)
    [ ask one-of patches with [distancexy 0 0 < 30]
      [ if (random-float 1 < (kpi * 1000)) [sprout-parties 1 [initialize-party] ]]
    [ create-parties 1 [set heading random-float 360 jump random-float 30 initialize-party] ]
        update-support

end