Fix lint

Author: pquentin

elasticsearch/exceptions.py

@@ -61,7 +61,7 @@ def __str__(self) -> str:
             if self.body and isinstance(self.body, dict) and "error" in self.body:
                 if isinstance(self.body["error"], dict):
                     root_cause = self.body["error"]["root_cause"][0]
-                    caused_by = self.body["error"].get("caused_by")
+                    caused_by = self.body["error"].get("caused_by", {})
                     cause = ", ".join(
                         filter(
                             None,