Block Pull request merge if fixVersion is blank

[Aishwarya Ralladoddi]

I'm trying to write a script to block a pull request merge for a story/bug for a particular project if fixVersion field is blank. We use Bitbucket v4.9.1 and already have few scripts under script pre-hooks. Is it possible for me to add a script here or should I have the "Custom Merge Check". Can I still use 'mergeRequest.veto' with this version ? 

[Aron Gombas _Midori_]

You can do this with a merge check policy (using the Commit Policy app).

The policy should contain a JQL condition which uses the JQL query "fixVersion is not empty". That's it.