# \[Event Registry\] Is there a way to check a correlation parameter for not being null?

**URL:** <https://forum.flowable.org/t/event-registry-is-there-a-way-to-check-a-correlation-parameter-for-not-being-null/6559>\
**Category:** Flowable Engine\
**Created:** [August 19, 2020, 1:59pm UTC](https://forum.flowable.org/t/event-registry-is-there-a-way-to-check-a-correlation-parameter-for-not-being-null/6559 "2020-08-19T13:59:53Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![aleksandrs](https://avatars.discourse-cdn.com/v4/letter/a/db5fbb/32.png) [@aleksandrs](https://forum.flowable.org/u/aleksandrs)\
**Post date:** [August 19, 2020, 1:59pm UTC](https://forum.flowable.org/t/event-registry-is-there-a-way-to-check-a-correlation-parameter-for-not-being-null/6559/1 "2020-08-19T13:59:53Z")

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![image](https://canada1.discourse-cdn.com/flex035/uploads/flowable/original/2X/b/b999d642b617c4c3d0142be9c9924061c2515892.png)

I have an event task block, it sends a message and then starts listening for a message. I want to define its correlation parameters so that the task is only triggered when specified variables are received(i.e., are not null).

Is there a way to do that ?

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**Author:** ![joram](https://yyz1.discourse-cdn.com/flex035/user_avatar/forum.flowable.org/joram/32/26_2.png) [@joram](https://forum.flowable.org/u/joram)\
**Post date:** [August 20, 2020, 8:51pm UTC](https://forum.flowable.org/t/event-registry-is-there-a-way-to-check-a-correlation-parameter-for-not-being-null/6559/2 "2020-08-20T20:51:15Z")

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The correlation only works on specific values, because it calculates a unique key based on the value to be able to do a performant lookup. So a _any match, but not null_ is not supported.