fix(annotators): avoid divide-by-zero in HeatMapAnnotator on empty detections

[Ace3Z]

Calling HeatMapAnnotator.annotate(...) on a fresh annotator with empty detections (e.g. the first few frames of a video before the model produces output) raises RuntimeWarning: invalid value encountered in divide. self.heat_mask is all zeros, so temp / temp.max() divides by zero, and the resulting nan/inf flows through the rest of the function.

Minimal repro:

import warnings
import numpy as np
import supervision as sv

warnings.simplefilter("error", RuntimeWarning)
annotator = sv.HeatMapAnnotator()
scene = np.zeros((100, 100, 3), dtype=np.uint8)
annotator.annotate(scene=scene, detections=sv.Detections.empty())
# RuntimeWarning: invalid value encountered in divide

Skip the normalisation step when temp.max() == 0; the resulting all-zero temp filters out via the self.heat_mask.astype(np.uint8) > 0 mask check below, so the scene is returned unchanged.

tests/annotators/test_core.py::TestHeatMapAnnotator::test_annotate_with_no_detections_does_not_warn covers the regression: it converts RuntimeWarning to an error and asserts the call succeeds with the scene unchanged.

[CLAassistant]

All committers have signed the CLA.

[Copilot]

Pull request overview

This PR fixes a RuntimeWarning: invalid value encountered in divide in HeatMapAnnotator.annotate(...) when called with empty detections on a fresh annotator, ensuring the scene is returned unchanged without emitting warnings.

Changes:

• Guard heatmap normalization to avoid dividing by zero when the heatmask maximum is 0.
• Add a regression test that converts RuntimeWarning to an error and verifies empty detections do not warn and do not modify the scene.

Quality Assessment (n/5):

• Code quality: 4/5
• Testing: 5/5
• Documentation: 5/5

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/supervision/annotators/core.py	Skips normalization when temp.max() == 0 to prevent divide-by-zero warnings on empty heat masks.
tests/annotators/test_core.py	Adds a regression test ensuring HeatMapAnnotator does not warn and returns an unchanged image on empty detections.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78%. Comparing base (fb2dec9) to head (3acea90).

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #2269   +/-   ##
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  Coverage       78%     78%           
=======================================
  Files           66      66           
  Lines         8410    8412    +2     
=======================================
+ Hits          6552    6580   +28     
+ Misses        1858    1832   -26     

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[Ace3Z]

Thanks for the autofix, the regression test still passes locally.