Throw when calling abstract methods; fix abstract return types

src/ol/render/ReplayGroup.js

@@ -1,6 +1,8 @@
 /**
  * @module ol/render/ReplayGroup
  */
+import {abstract} from '../util.js';
+
 /**
  * Base class for replay groups.
  */
@@ -11,20 +13,26 @@ class ReplayGroup {
    * @param {import("./ReplayType.js").default} replayType Replay type.
    * @return {import("./VectorContext.js").default} Replay.
    */
-  getReplay(zIndex, replayType) {}
+  getReplay(zIndex, replayType) {
+    return abstract();
+  }
 
   /**
    * @abstract
    * @return {boolean} Is empty.
    */
-  isEmpty() {}
+  isEmpty() {
+    return abstract();
+  }
 
   /**
    * @abstract
    * @param {boolean} group Group with previous replay
    * @return {Array<*>} The resulting instruction group
    */
-  addDeclutter(group) {}
+  addDeclutter(group) {
+    return abstract();
+  }
 }
 
 export default ReplayGroup;