Prevent calls to getLayoutProperty from causing fatal error when layer doesn't exist

src/style/style.js

@@ -786,12 +786,18 @@ class Style extends Evented {
 
     /**
      * Get a layout property's value from a given layer
-     * @param {string} layer the layer to inspect
+     * @param {string} layerId the layer to inspect
      * @param {string} name the name of the layout property
      * @returns {*} the property value
      */
-    getLayoutProperty(layer: string, name: string) {
-        return this.getLayer(layer).getLayoutProperty(name);
+    getLayoutProperty(layerId: string, name: string) {
+        const layer = this.getLayer(layerId);
+        if (!layer) {
+            this.fire(new ErrorEvent(new Error(`The layer '${layerId}' does not exist in the map's style.`)));
+            return;
+        }
+
+        return layer.getLayoutProperty(name);
     }
 
     setPaintProperty(layerId: string, name: string, value: any) {

test/unit/ui/map.test.js

@@ -1231,6 +1231,28 @@ test('Map', (t) => {
         t.end();
     });
 
+    t.test('#getLayoutProperty', (t) => {
+        t.test('fires an error if layer not found', (t) => {
+            const map = createMap(t, {
+                style: {
+                    version: 8,
+                    sources: {},
+                    layers: []
+                }
+            });
+
+            map.on('style.load', () => {
+                map.on('error', ({ error }) => {
+                    t.match(error.message, /does not exist in the map\'s style/);
+                    t.end();
+                });
+                map.getLayoutProperty('non-existant', 'text-transform', 'lowercase');
+            });
+        });
+
+        t.end();
+    });
+
     t.test('#setPaintProperty', (t) => {
         t.test('sets property', (t) => {
             const map = createMap(t, {