Task list getters explicitly check for null now

Issue: SPR-13680

Author: jhoeller

spring-context/src/main/java/org/springframework/scheduling/config/ScheduledTaskRegistrar.java

@@ -130,7 +130,7 @@ public void setTriggerTasksList(List<TriggerTask> triggerTasks) {
 	 * @since 4.2
 	 */
 	public List<TriggerTask> getTriggerTaskList() {
-		return Collections.unmodifiableList(this.triggerTasks);
+		return (this.triggerTasks != null? Collections.unmodifiableList(this.triggerTasks) : null);
 	}
 
 	/**
@@ -159,7 +159,7 @@ public void setCronTasksList(List<CronTask> cronTasks) {
 	 * @since 4.2
 	 */
 	public List<CronTask> getCronTaskList() {
-		return Collections.unmodifiableList(this.cronTasks);
+		return (this.cronTasks != null ? Collections.unmodifiableList(this.cronTasks) : null);
 	}
 
 	/**
@@ -188,7 +188,7 @@ public void setFixedRateTasksList(List<IntervalTask> fixedRateTasks) {
 	 * @since 4.2
 	 */
 	public List<IntervalTask> getFixedRateTaskList() {
-		return Collections.unmodifiableList(this.fixedRateTasks);
+		return (this.fixedRateTasks != null ? Collections.unmodifiableList(this.fixedRateTasks) : null);
 	}
 
 	/**
@@ -217,7 +217,7 @@ public void setFixedDelayTasksList(List<IntervalTask> fixedDelayTasks) {
 	 * @since 4.2
 	 */
 	public List<IntervalTask> getFixedDelayTaskList() {
-		return Collections.unmodifiableList(this.fixedDelayTasks);
+		return (this.fixedDelayTasks != null ? Collections.unmodifiableList(this.fixedDelayTasks) : null);
 	}
 
 	/**