diff --git a/lidar_pipeline/webapp.py b/lidar_pipeline/webapp.py
index effca3a..7985f70 100644
--- a/lidar_pipeline/webapp.py
+++ b/lidar_pipeline/webapp.py
@@ -441,10 +441,10 @@ def _viz_step_labels():
 
 
 class PreviewRequest(BaseModel):
-    bbox: list = Field(None, description="[ouest, sud, est, nord] en WGS84 "
+    bbox: Optional[list] = Field(None, description="[ouest, sud, est, nord] en WGS84 "
                      "(requis sauf all_missing=true)")
     regenerate: bool = Field(False, description="Inclure les tuiles déjà générées")
-    viz: list = Field(None,
+    viz: Optional[list] = Field(None,
                       description="Visualisations demandées, noms d'étapes du "
                                   "pipeline (ex: aspect, wavelet) ; défaut : aspect. "
                                   "Une tuile existante est considérée faite "