Netlogo - Ordered Movement - netlogo

Question

I have the following error in Netlogo and I'm unsure why. I am trying to make the turtles move around in a ordered fashion but I keep getting an error when I change the d angle: "FACE expected input to be an agent but got NOBODY instead".
Any help would be appreciated.
globals [Angles]
to setup
clear-all
create-turtles amount [ setxy random-xcor random-ycor ]
ask turtles [
set Angles (random 360)
]
reset-ticks
end
to monitor
show count patches
show ticks
end
to go
if (all? patches [pcolor = yellow]) [stop]
ask turtles [
face min-one-of patches with [ pcolor = black ] [ distance myself ]
;; This line of code tells the turtle to head towards the nearest patch containing the colour of black.
set Angle d Angle * 1 - Angle
rightt Angle
forwardd 1
ifelse show-travel-line? [pen-down][pen-up]
set color red
if pcolor = black [
set pcolor yellow
]
]
tick
end

Answer 1

You can unveil the problem but running this test:
to test
ca
crt 1
let x -10E307 * 10
show x
ask turtle 0 [rt x]
inspect turtle 0
end
You will see that the heading is NaN because you gave it a turn of -Infinity. Now if you move the turtle, the xcor and ycor will become Nan.
To avoid this problem, you need to limit the values taken by angle. For example,
globals [turn angle]
to setup
clear-all
set turn random-float 1
create-turtles 10 [
setxy random-xcor random-ycor
set color red
pen-down
]
reset-ticks
end
to go
if (all? patches [pcolor = yellow]) [stop]
ask turtles [
part1
part2
if pcolor = black [
set pcolor yellow
]
]
tick
end
to part1
let _patches (patches with [ pcolor = black ])
face min-one-of _patches [ distance myself ]
end
to part2
set turn (4 * turn * (1 - turn))
set angle turn * 360
rt angle
fd 1
end