A style function missing return drops most features

• Only the 120 features with status 'alarm' render; the other 680 disappear from the map.
• Uncaught TypeError: Cannot read properties of undefined (reading 'getType') at executeDeclutter (VectorLayer.js:1268).
• layer.getStyleFunction()(feature, resolution) prints undefined for a normal feature.

1. Call layer.getStyleFunction() on a few features and print the returned value.
2. Check every branch of the style function for an explicit return.
3. Check whether null is used where not-rendered is intended.
4. Check whether declutter is enabled, since it turns undefined into a thrown error.

Return an ol.style.Style for each branch and return null explicitly for hidden features, pre-building the style objects once outside the callback instead of creating them per feature.

Uncaught TypeError: Cannot read properties of undefined (reading 'getType')
    at executeDeclutter (VectorLayer.js:1268)

var styleFn = layer.getStyleFunction();
features.slice(0, 5).forEach(function (f) {
  var s = styleFn(f, map.getView().getResolution());
  console.log(f.get('status'), s && s.length, s);
});
// alarm 1
// normal undefined    ← 问题所在

• Returning undefined instead of null looks the same in source but crashes declutter and skips rendering.
• Constructing new ol.style.Style inside the function for 800 features each frame causes GC pressure and slow redraws.