src/models/entities/RunnerGroup.ts

@@ -51,6 +51,9 @@ export abstract class RunnerGroup {
   */
   @IsInt()
   public get distance(): number {
+    if (!this.runners || this.runners.length == 0) {
+      return 0;
+    }
     return this.runners.reduce((sum, current) => sum + current.distance, 0);
   }