make document handling thread safe when requesting information.

src/main/java/uk/gov/hmcts/probate/service/InformationRequestCorrespondenceService.java

@@ -7,7 +7,6 @@
 import uk.gov.hmcts.probate.model.ccd.raw.request.CaseDetails;
 import uk.gov.service.notify.NotificationClientException;
 
-import java.util.ArrayList;
 import java.util.List;
 
 import static uk.gov.hmcts.probate.model.State.CASE_STOPPED_REQUEST_INFORMATION;
@@ -18,18 +17,16 @@
 public class InformationRequestCorrespondenceService {
 
     private final NotificationService notificationService;
-    private List<Document> documents;
 
     public List<Document> emailInformationRequest(CaseDetails caseDetails) {
-        documents = new ArrayList<>();
         try {
-            documents.add(notificationService
-                    .sendEmail(CASE_STOPPED_REQUEST_INFORMATION, caseDetails));
-            log.info("Successful response for request for information email for case id {} ",
-                    caseDetails.getId());
+            final Document notification = notificationService.sendEmail(CASE_STOPPED_REQUEST_INFORMATION, caseDetails);
+            log.info("Successful response for request for information email for case id {} ", caseDetails.getId());
+            return List.of(notification);
         } catch (NotificationClientException e) {
             log.error(e.getMessage());
+            // this feels wrong - do we not want to alert the caller that the email sending has failed?
+            return List.of();
         }
-        return documents;
     }
 }