fix: chart import validation (#26993)

superset/utils/core.py

@@ -1415,6 +1415,15 @@ def split_adhoc_filters_into_base_filters(  # pylint: disable=invalid-name
         form_data["filters"] = simple_where_filters
 
 
+def get_user() -> User | None:
+    """
+    Get the current user (if defined).
+
+    :returns: The current user
+    """
+    return g.user if hasattr(g, "user") else None
+
+
 def get_username() -> str | None:
     """
     Get username (if defined) associated with the current user.