refactor: moved default price into SCPriceGroup

src/core/base/ThingThatCanBeOffered.ts

@@ -20,10 +20,13 @@ import {SCISO8601Date} from '../types/Time';
 import {SCInPlace} from './../types/Places';
 
 /**
- * A map from group name to price
+ * Default price without distinction
  */
 export interface SCPriceGroup {
-  [s: string]: number | undefined;
+  /**
+   * Default price of the thing
+   */
+  default: number;
 }
 
 /**
@@ -82,15 +85,10 @@ export interface SCThingThatCanBeOfferedOffer<T extends SCPriceGroup>
    */
   availabilityStarts?: SCISO8601Date;
 
-  /**
-   * Default price of the thing
-   */
-  price: number;
-
   /**
    * List of prices that are distinct for specific groups
    */
-  prices?: T;
+  prices: T;
 
   /**
    * Provider of an offer

src/core/things/DateSeries.ts

@@ -32,7 +32,7 @@ export interface SCSportCoursePriceGroup extends SCAcademicPriceGroup {
   /**
    * Price for alumnis
    */
-  alumni: number;
+  alumni?: number;
 }
 
 /**