On 7.7.4 I can do it using the menu “Development” → “Manage Groovy Scripts…” but I cannot find it on 7.8.0 anymore which is odd because I cannot find anything in the release note . It looks like a bug, could you report the issue on the JIRA tracker to follow up?
In the meantime, I suggest that you downgrade to 7.7 to avoid the problem.
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