diff --git a/src/workflow_app/workflow/states.py b/src/workflow_app/workflow/states.py
index e4ca05a3..d4deef0f 100644
--- a/src/workflow_app/workflow/states.py
+++ b/src/workflow_app/workflow/states.py
@@ -53,7 +53,11 @@ def _call_db_task(self, task_data, headers, message):
         :param message: JSON-encoded message content
         """
         task_def = json.loads(task_data)
-        if "task_class" in task_def and len(task_def["task_class"].strip()) > 0:
+        if (
+            "task_class" in task_def
+            and (task_def["task_class"] is not None)
+            and len(task_def["task_class"].strip()) > 0
+        ):
             try:
                 toks = task_def["task_class"].strip().split(".")
                 module = ".".join(toks[: len(toks) - 1])
diff --git a/src/workflow_app/workflow/tests/test_states.py b/src/workflow_app/workflow/tests/test_states.py
index 9d1397f5..899fda85 100644
--- a/src/workflow_app/workflow/tests/test_states.py
+++ b/src/workflow_app/workflow/tests/test_states.py
@@ -26,10 +26,26 @@ def test_call_db_task(self):
         message = "test_msg"
         sa._call_db_task(task_data, headers, message)
 
-    def test_call(self):
-        # NOTE: the decorator logged_action is preventing unittest mock from
-        #       isolating the functionality for unit test, hence skipping
-        pass
+    @mock.patch("workflow.states.transactions.get_task")
+    def test_call(self, mock_get_task):
+        # NOTE: skipping testing of importing a task class as this option is not currently used
+        from workflow.states import StateAction
+
+        mock_connection = mock.Mock()
+        sa = StateAction(connection=mock_connection, use_db_task=True)
+        headers = {"destination": "test", "message-id": "test-0"}
+        message = '{"facility": "SNS", "instrument": "arcs", "ipts": "IPTS-5", "run_number": 3, "data_file": "test"}'
+
+        # test with task class: null
+        mock_get_task.return_value = '{"task_class": null, "task_queues": ["QUEUE-0", "QUEUE-1"]}'
+        sa(headers, message)
+        assert mock_connection.send.call_count == 2  # one per task queue
+        original_call_count = mock_connection.send.call_count
+
+        # test with task class: empty string
+        mock_get_task.return_value = '{"task_class": "", "task_queues": ["QUEUE-0", "QUEUE-1"]}'
+        sa(headers, message)
+        assert mock_connection.send.call_count - original_call_count == 2  # one per task queue
 
     @mock.patch("workflow.database.transactions.add_status_entry")
     def test_send(self, mockAddStatusEntry):