block invalid variable name (#2504)

backport from develop
resolves #2500

Co-authored-by: Fred Lefévère-Laoide <[email protected]>

Author: FredLL-Avaiga

taipy/gui/gui.py

@@ -674,7 +674,7 @@ def __front_end_update(
         rel_var: t.Optional[str] = None,
         on_change: t.Optional[str] = None,
     ) -> None:
-        if not var_name:
+        if not var_name or "." in var_name:
             return
         # Check if Variable is a managed type
         current_value = _getscopeattr_drill(self, self.__evaluator.get_hash_from_expr(var_name))