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Click on the Create issue.
Create an issue without assigning it to someonea user.
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It will show the below Error error message which was defined when adding the expression and error message in the validator when validation fails.
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Now assign the issue to any user and create it. It will not show the error message.
Next page:
https://confluence.prod.mgtechsoft.com/wiki/spaces/EFJ/pages/edit-v2/3057680385