fix: issue 226 (#227)

Checking if the TaskUpdate has an update message before trying to
convert it.

Fixes #226 🦕

Signed-off-by: Emmanuel Hugonnet <ehugonne@redhat.com>
Co-authored-by: Aleksey Ivashin <xumuk123@mail.ru>

Author: ehsavoie

spec-grpc/src/main/java/io/a2a/grpc/utils/ProtoUtils.java

@@ -889,8 +889,11 @@ private static DataPart dataPart(io.a2a.grpc.DataPart dataPart) {
         }
 
         private static TaskStatus taskStatus(io.a2a.grpc.TaskStatus taskStatus) {
-            return new TaskStatus(
-                    taskState(taskStatus.getState()),
+            TaskState state = taskState(taskStatus.getState());
+            if (state == null) {
+                return null;
+            }
+            return new TaskStatus(state,
                     taskStatus.hasUpdate() ? message(taskStatus.getUpdate()) : null,
                     OffsetDateTime.ofInstant(Instant.ofEpochSecond(taskStatus.getTimestamp().getSeconds(), taskStatus.getTimestamp().getNanos()), ZoneOffset.UTC)
             );