With the recent changes in QMacStyle a manual slider rendering was introduced for QSlider to address issues on macOS 26. This triggered an assert on the graphics context being nullptr in the style sheet auto-test, the one that creates a QImage-based QPainter with image format QImage::Format_ARGB32. Creating a bitmap CGContextRef (CGBitmapCreateContext) with such format fails on macOS (and asserts in 'drawSliderKnob' function on Tahoe, potentially generating warnings on CoreGraphics side when using NSControls). Protection against such context is needed in QMacStyle.