fix problems with event rendering parsing

packages/core/src/component/event-ui.ts

@@ -97,7 +97,7 @@ export function processScopedUiProps(prefix: string, rawScoped: any, calendar: C
 }
 
 const EMPTY_EVENT_UI: EventUi = {
-  rendering: '',
+  rendering: null,
   startEditable: null,
   durationEditable: null,
   constraints: [],
@@ -116,7 +116,7 @@ export function combineEventUis(uis: EventUi[]): EventUi {
 
 function combineTwoEventUis(item0: EventUi, item1: EventUi): EventUi { // hash1 has higher precedence
   return {
-    rendering: item1.rendering || item0.rendering,
+    rendering: item1.rendering != null ? item1.rendering : item0.rendering,
     startEditable: item1.startEditable != null ? item1.startEditable : item0.startEditable,
     durationEditable: item1.durationEditable != null ? item1.durationEditable : item0.durationEditable,
     constraints: item0.constraints.concat(item1.constraints),

packages/core/src/structs/event.ts

@@ -61,12 +61,11 @@ export interface EventTuple {
 export type EventInstanceHash = { [instanceId: string]: EventInstance }
 export type EventDefHash = { [defId: string]: EventDef }
 
-export const NON_DATE_PROPS = {
+export const NON_DATE_PROPS = { // ...that are NOT in the EventUi object
   id: String,
   groupId: String,
   title: String,
   url: String,
-  rendering: String,
   extendedProps: null
 }