Features used to implement the example

• Boolean Validator with math, date-time or text-string termsField "Resolution", which is represented by field code %{00028}
• Function "linkedIssues(string issue_link_types) : issue list", which returns the list of issues linked to current one using issue link types in argument issue_link_types. Argument issue_link_types is a comma separated list of issue link type names, or an empty string ("") for representing all issue link types, i.e., linkedIssues("") is equivalent to linkedIssues().
• Function "count(issue list l) : number", which returns the number of issues in l.

Example: Require at least one "duplicates" issue link when resolution = "Duplicate"

When we resolve an issue setting Resolution as "Duplicate", we would like to enforce existence of at least one linked issue with issue link type "duplicates".

We use Boolean Validator with math, date-time or text-string terms with the following configuration:

Text to be parsed is: % %{00028} != "Duplicate" OR count(linkedIssues("duplicates")) > 0 

Once configured, transition "Resolve Issue" will look like this:

Alternative expression

Since version 2.1.22, logical connective IMPLIES is available. Using it, an equivalent expression can be written like this: 

%{00028} = "Duplicate" IMPLIES count(linkedIssues("duplicates")) > 0