b78aed99ea
While it is not easily possible to create a ConcurrentTaskScheduler with no scheduled executor, DefaultManagedTaskScheduler has a default constructor that does that as the JNDI lookup happens in the regular afterPropertiesSet callback. If such an instance is created manually, it can throw an unhelpful NullPointerException if one attempts to schedule a task. This commit updates ConcurrentTaskScheduler to flag that the scheduled executor could be `null` and check if that's the case before using it. This now throws a dedicated exception that should hopefully provide better context for those upgrading. See gh-27914 Closes gh-31751
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