[#4340] Fixes possible access to undefined object (#4431)

* [#4340] Fixes possible access to undefined object

* CHANGELOG update

* Adds the test

CHANGELOG.md

@@ -8,6 +8,7 @@
 ### 🐞 Bug fixes
 
 - Fix lag on fast map zoom ([#4366](https://github.com/maplibre/maplibre-gl-js/pull/4366))
+- Fix unguarded read access to possibly undefined object ([#4431](https://github.com/maplibre/maplibre-gl-js/pull/4431))
 - Fix remove hash string when map is removed ([#4427](https://github.com/maplibre/maplibre-gl-js/pull/4427))
 - _...Add new stuff here..._
 

src/render/painter.test.ts

@@ -0,0 +1,51 @@
+import {TerrainSpecification} from '@maplibre/maplibre-gl-style-spec';
+
+import {Painter} from './painter';
+import {Transform} from '../geo/transform';
+import {Style} from '../style/style';
+import {Evented} from '../util/evented';
+import {RequestManager} from '../util/request_manager';
+
+class StubMap extends Evented {
+    style: Style;
+    transform: Transform;
+    private _requestManager: RequestManager;
+    _terrain: TerrainSpecification;
+
+    constructor() {
+        super();
+        this.transform = new Transform();
+        this._requestManager = new RequestManager();
+    }
+
+    _getMapId() {
+        return 1;
+    }
+
+    getPixelRatio() {
+        return 1;
+    }
+
+    setTerrain(terrain) { this._terrain = terrain; }
+    getTerrain() { return this._terrain; }
+}
+
+const getStubMap = () => new StubMap() as any;
+
+test('Render must not fail with incompletely loaded style', () => {
+    const gl = document.createElement('canvas').getContext('webgl');
+    const transform = new Transform(0, 22, 0, 60, true);
+    const painter = new Painter(gl, transform);
+    const map = getStubMap();
+    const style = new Style(map);
+    style._updatePlacement(transform, false, 0, false);
+    painter.render(style, {
+        fadeDuration: 0,
+        moving: false,
+        rotating: false,
+        showOverdrawInspector: false,
+        showPadding: false,
+        showTileBoundaries: false,
+        zooming: false,
+    });
+});

src/render/painter.ts

@@ -409,7 +409,7 @@ export class Painter {
         this.clearStencil();
 
         // draw sky first to not overwrite symbols
-        if (this.style.stylesheet.sky) drawSky(this, this.style.sky);
+        if (this.style.stylesheet?.sky) drawSky(this, this.style.sky);
 
         this._showOverdrawInspector = options.showOverdrawInspector;
         this.depthRangeFor3D = [0, 1 - ((style._order.length + 2) * this.numSublayers * this.depthEpsilon)];