set default to "" while extracting basis

csst_dag/dag/_dispatcher.py

@@ -116,7 +116,7 @@ def override_common_keys(d1: dict, d2: dict) -> dict:
 
 def extract_basis_table(dlist: list[dict], basis_keys: tuple) -> table.Table:
     """Extract basis key-value pairs from a list of dictionaries."""
-    return table.Table([{k: d.get(k) for k in basis_keys} for d in dlist])
+    return table.Table([{k: d.get(k, default="") for k in basis_keys} for d in dlist])
 
 
 def split_data_basis(data_basis: table.Table, n_split: int = 1) -> list[table.Table]:
@@ -573,7 +573,7 @@ class Dispatcher:
         plan_basis: table.Table,
         data_basis: table.Table,
         # n_jobs: int = 1,
-    ):
+    ) -> list[dict]:
         # return an empty list if input is empty
         if len(plan_basis) == 0 or len(data_basis) == 0:
             return []