diff --git a/testkitbackend/_async/requests.py b/testkitbackend/_async/requests.py
index 7493c7e5..4653a488 100644
--- a/testkitbackend/_async/requests.py
+++ b/testkitbackend/_async/requests.py
@@ -536,18 +536,18 @@ def __init__(self, session):
 
 async def NewSession(backend, data):
     driver = backend.drivers[data["driverId"]]
-    access_mode = data["accessMode"]
     expected_warnings = []
-    if access_mode == "r":
-        access_mode = neo4j.READ_ACCESS
-    elif access_mode == "w":
-        access_mode = neo4j.WRITE_ACCESS
-    else:
-        raise ValueError("Unknown access mode:" + access_mode)
     config = {
-        "default_access_mode": access_mode,
         "database": data["database"],
     }
+    access_mode = data["accessMode"]
+    if access_mode is not None:
+        if access_mode == "r":
+            config["default_access_mode"] = neo4j.READ_ACCESS
+        elif access_mode == "w":
+            config["default_access_mode"] = neo4j.WRITE_ACCESS
+        else:
+            raise ValueError("Unknown access mode:" + access_mode)
     if data.get("bookmarks") is not None:
         config["bookmarks"] = neo4j.Bookmarks.from_raw_values(
             data["bookmarks"]
diff --git a/testkitbackend/_sync/requests.py b/testkitbackend/_sync/requests.py
index 258b116a..a70bbc65 100644
--- a/testkitbackend/_sync/requests.py
+++ b/testkitbackend/_sync/requests.py
@@ -536,18 +536,18 @@ def __init__(self, session):
 
 def NewSession(backend, data):
     driver = backend.drivers[data["driverId"]]
-    access_mode = data["accessMode"]
     expected_warnings = []
-    if access_mode == "r":
-        access_mode = neo4j.READ_ACCESS
-    elif access_mode == "w":
-        access_mode = neo4j.WRITE_ACCESS
-    else:
-        raise ValueError("Unknown access mode:" + access_mode)
     config = {
-        "default_access_mode": access_mode,
         "database": data["database"],
     }
+    access_mode = data["accessMode"]
+    if access_mode is not None:
+        if access_mode == "r":
+            config["default_access_mode"] = neo4j.READ_ACCESS
+        elif access_mode == "w":
+            config["default_access_mode"] = neo4j.WRITE_ACCESS
+        else:
+            raise ValueError("Unknown access mode:" + access_mode)
     if data.get("bookmarks") is not None:
         config["bookmarks"] = neo4j.Bookmarks.from_raw_values(
             data["bookmarks"]