# Mutate add\_field gives sprint f format for nil values. How to solve this?

**URL:** https://discuss.elastic.co/t/mutate-add-field-gives-sprint-f-format-for-nil-values-how-to-solve-this/181473
**Category:** Logstash
**Created:** [May 16, 2019, 7:58pm UTC](https://discuss.elastic.co/t/mutate-add-field-gives-sprint-f-format-for-nil-values-how-to-solve-this/181473 "2019-05-16T19:58:28Z")
**Posts on this page:** 1
**Showing post:** 4

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### Author: ![Badger](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/badger/32/25190_2.png) [@Badger](https://discuss.elastic.co/u/Badger)
#### Post date: [May 16, 2019, 8:38pm UTC](https://discuss.elastic.co/t/mutate-add-field-gives-sprint-f-format-for-nil-values-how-to-solve-this/181473/4 "2019-05-16T20:38:13Z")

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OK, so that event does not have a [Bugs][CloserName] field, so you should expect the mutate to leave it with the sprintf reference. You could use something like [this](https://discuss.elastic.co/t/removing-fields-with-certain-value-or-if-mapping-is-not-found-from-the-output/180941/2) to remove any fields whose value starts with "%{".

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