If you want to run a JQL query to return Jira Issue ID (Key) values from a search, you can use the following JQL Utility Function:

import com.atlassian.jira.component.ComponentAccessor
import com.atlassian.jira.issue.search.SearchProvider
import com.atlassian.jira.jql.parser.JqlQueryParser
import com.atlassian.jira.web.bean.PagerFilter
 
def findIssues(String jqlQuery) {
    def issueManager = ComponentAccessor.issueManager
    def user = ComponentAccessor.jiraAuthenticationContext.user
    def jqlQueryParser = ComponentAccessor.getComponent(JqlQueryParser.class)
    def searchProvider = ComponentAccessor.getComponent(SearchProvider.class)
    def query = jqlQueryParser.parseQuery(jqlQuery)
    def results = searchProvider.search(query, user, PagerFilter.unlimitedFilter)
    results.issues.collect { issue -> issueManager.getIssueObject(issue.id) }
}
 
def issues = findIssues('project = PROJKEY')
if ( ! issues) {
//return true if no issues found
    return true
}
else
    return false