diff --git a/telethon/tl/session.py b/telethon/tl/session.py
index dc1b13ed..ee5f1091 100644
--- a/telethon/tl/session.py
+++ b/telethon/tl/session.py
@@ -104,24 +104,24 @@ class JsonSession:
            those required to init a connection will be copied.
         """
         # These values will NOT be saved
-        if isinstance(session_user_id, str):
-            self.session_user_id = session_user_id
-
-            # For connection purposes
-            self.device_model = platform.node()
-            self.system_version = platform.system()
-            self.app_version = '1.0'  # note: '0' will provoke error
-            self.lang_code = 'en'
-
-        elif isinstance(session_user_id, JsonSession):
+        if isinstance(session_user_id, JsonSession):
             self.session_user_id = None
 
+            # For connection purposes
             session = session_user_id
             self.device_model = session.device_model
             self.system_version = session.system_version
             self.app_version = session.app_version
             self.lang_code = session.lang_code
 
+        else:  # str / None
+            self.session_user_id = session_user_id
+
+            self.device_model = platform.node()
+            self.system_version = platform.system()
+            self.app_version = '1.0'  # note: '0' will provoke error
+            self.lang_code = 'en'
+
         # Cross-thread safety
         self._lock = Lock()