Strange artifact in pdf file

[AvivEsh]

Hello, I have created an open shape with 3 lines and the exported pdf, at least in Acrobat Reader comes out like this (added in the attached image).

The pdf gathered using pymupdf of the path is the following:
{'items': [('l', Point(817.3600463867188, 285.72003173828125), Point(931.9600219726562, 285.72003173828125)), ('l', Point(931.9600219726562, 285.72003173828125), Point(931.9600219726562, 307.800048828125)), ('l', Point(824.2000122070312, 307.800048828125), Point(931.9600219726562, 307.800048828125))], 'type': 'f', 'even_odd': False, 'fill_opacity': 1.0, 'fill': (0.0, 0.0, 0.0), 'rect': Rect(817.3600463867188, 285.72003173828125, 931.9600219726562, 307.800048828125), 'seqno': 0, 'layer': '', 'closePath': None, 'color': None, 'width': None, 'lineCap': None, 'lineJoin': None, 'dashes': None, 'stroke_opacity': None}

Can I change something in the properties so I just get 3 lines without this weird black triangle in the middle?
Thank you in advance.

[JorjMcKie]

You are keeping a few things as secrets unfortunately (😉):

1. The PDF / page upon you were drawing
2. The script you were using

The extracted vector graphics at least is a filled black rectangle and complies with the image(s) you have attached 🤷‍♂️.

[AvivEsh]

Well you are right. I add here the pdf file that contains the original geometry.
The reason I did not put the script is because it is very long. Essentially I cut some existing lines and eliminate others by considering some parameters.

The main thing I want to know is how is it possible now that my shape is not 'closed', not to be filled in its interior.
beforer.pdf

[JorjMcKie]

Avoid using a fill color is the easiest recipe. This snippet draws a triangle without fill color:

import pymupdf

doc = pymupdf.open()
page = doc.new_page()
page.draw_polyline(((100, 100), (200, 200), (100, 200)), closePath=True)
doc.ez_save("triangle.pdf")

[AvivEsh]

so fill color is the culprit? because I cannot directly change the type of the path (correct me if I am wrong)

[JorjMcKie]

exactly - I wrote that stuff 😎