Verify optional message is not missing or a literal "null" value

Author: tdonohue

dspace-server-webapp/src/main/java/org/dspace/app/rest/repository/RequestItemRepository.java

@@ -242,7 +242,10 @@ public RequestItemRest put(Context context, HttpServletRequest request,
         }
 
         JsonNode responseMessageNode = requestBody.findValue("responseMessage");
-        String message = responseMessageNode.asText();
+        String message = null;
+        if (responseMessageNode != null && !responseMessageNode.isNull()) {
+            message = responseMessageNode.asText();
+        }
 
         ri.setDecision_date(new Date());
         requestItemService.update(context, ri);