IssueLinksSystemField.IssueLinkingValue issueLinkingValue = ((IssueLinksSystemField.IssueLinkingValue) issue.getExternalFieldValue("issuelinks"));
List<String> keys = (List<String>) issueLinkingValue.getValidationResult().getLinkKeys();
IssueLinksSystemField.IssueLinkingValue issueLinkingValue = ((IssueLinksSystemField.IssueLinkingValue) issue.getExternalFieldValue("issuelinks"));
List<String> keys = (List<String>) issueLinkingValue.getValidationResult().getLinkKeys();