I am not a programmer but trying to put code in the plugin
import com.atlassian.jira.bc.issue.search.SearchService;
import com.atlassian.jira.bc.project.component.ProjectComponent;
import com.atlassian.jira.component.ComponentAccessor;
import com.atlassian.jira.project.Project;
import com.atlassian.jira.user.ApplicationUser;
import com.atlassian.jira.user.ApplicationUsers;
import com.atlassian.jira.web.bean.PagerFilter;
String iskey = issue.get("customfield_10500");
String jqlSearch = "summary ~ " + iskey;
SearchService searchService = ComponentAccessor.getComponentOfType(SearchService.class);
ParseResult parseResult = searchService.parseQuery(authenticationContext.getLoggedInUser(), jqlSearch);
int totalIssues = 0;
if (parseResult.isValid()) {
try {
SearchResults results = searchService.search(authenticationContext.getLoggedInUser(), parseResult.getQuery(), PagerFilter.getUnlimitedFilter());
final List<Issue> issues = results.getIssues();
totalIssues = issues.size();
return totalIssues;
} catch (SearchException e) {
e.printStackTrace();
}
}