Create road network from shapefile in netlogo

Question

I want to create a road network from Netlogo using a shapefile. My walkers are supposed to walk on roads to a specific goal. When I call the to go procedure I keep getting the error:

OF expected input to be an agent or agentset but got NOBODY instead.
error while walker 15 running OF
  called by procedure GO
  called by Button 'go'

My code so far is:

breed [nodes node]
breed [walkers walker]

walkers-own [
 origin
 myGoal
 wlocation  
]

to make-road-network
  clear-links
  let first-node nobody
  let previous-node nobody
  foreach gis:feature-list-of roads[ polyline ->
    foreach gis:vertex-lists-of  polyline [ segment ->
      foreach segment [coordinate ->
        let location gis:location-of coordinate
        if not empty? location [
          create-nodes 1 [
            set color blue
            set size 1
            set xcor item 0 location
            set ycor item 1 location
            set hidden? true
            if first-node = nobody [
              set first-node self
            ]
            if previous-node != nobody [
              create-link-with previous-node
            ]
            set previous-node self
          ]
        ]
      ]
      set previous-node nobody
    ]
  ]
  ; connect adjacent polylines/roads
  ask nodes [ create-links-with other nodes in-radius 0.001 ]
end


to go
  ask walkers[
    let new-location one-of [link-neighbors] of wlocation       ; here I am getting the error
    move-to new-location
    set wlocation new-location
    
  ]
end


to setupWalkers [nWalkers]
  sprout-walkers nWalkers  [
    set color 14
    set size 3 
    set shape "person"
    pen-down
    set origin  Spots
    set wlocation one-of nodes
    move-to wlocation
  ]
end

I followed the question (how to create moving turtles out of a shapefile in Netlogo) and used the code.

Answer 1

I could see two possible options for this error. The first possibility is that some nodes are not connected to any other nodes, but I don't know enough about the gis extension to comment on that.

The second possibility is that let new-location one-of [link-neighbors] of wlocation gives you the link-neighbors of your walker (which returns nobody), instead of the link-neighbors of your wlocation. The easy fix is to use brackets in order to specify whose link-neighbors you are interested in:

let new-location one-of ([link-neighbors] of wlocation)