patches-own
[
  owner  ;; turtle who claims patch for territory
  benefit  ;; i.e., food
  avoiding ;; turtle who is avoiding this patch
]

turtles-own
[
  start-patch  ;; my territory center
  destination  ;; my next patch to claim
  territory  ;; patches I own
  blacklist  ;; my agentset of patches to avoid
]

to pick-patch
    if patch-here = start-patch [ set destination highest-value ]
    if destination != nobody [ travel ]
end

to travel
     ;; there are a number of actions here, but the relevant one is:
     ;; check if owned, and avoid it:
     if patch-here != destination
          [ if owner != nobody  ;; if it's owned...
            [ if owner != self  ;; and not by me...
              [ avoid-obstacle
                move-to start-patch ]
            ]
          ]
end

to avoid-obstacle
     ask destination [ set avoiding myself ]
     set blacklist (patches with [avoiding = myself])
end

to-report highest-value            ;; <--- source of error since using "blacklist"
     let available-destinations edge-patches with [blacklist != myself]
     report max-one-of available-destinations ([benefit-to-me / cost-to-me])
end

to-report benefit-to-me
     report mean [benefit] of patches in-radius 2
end

to-report cost-to-me
     report distance [start-patch] of myself
end

to-report edge-patches
     report (patch-set [neighbors4] of territory) with [owner = nobody]
end

to-report highest-value
     let available-destinations edge-patches with [avoiding != myself]
     report max-one-of available-destinations ([benefit-to-me / cost-to-me])
end

to avoid-obstacle
      ask destination
        [ let now-avoiding myself
          set avoiding (turtle-set avoiding now-avoiding) ]
      set blacklist (patch-set blacklist patches with [avoiding = myself])
end