optional review label id

Author: msokoloff1

labelbox/data/serialization/labelbox_v1/label.py

@@ -110,7 +110,7 @@ class Review(BaseModel):
     id: str
     created_at: str
     created_by: str
-    label_id: str
+    label_id: Optional[str] = None
 
     class Config:
         alias_generator = camel_case
@@ -246,4 +246,4 @@ def _is_url(self) -> bool:
              "s3://")) or "tileLayerUrl" in self.row_data
 
     class Config:
-        allow_population_by_field_name = True
+        allow_population_by_field_name = True