raise key error if n_epec_frame is not found

csst_dag/dag/_dispatcher.py

@@ -158,10 +158,14 @@ class Dispatcher:
         qr = plan.find(**override_common_keys(PLAN_PARAMS, kwargs))
         assert qr.success, qr
         # plan basis / obsid basis
+        try:
             for _ in qr.data:
                 _["n_frame"] = (
                     _["params"]["n_epec_frame"] if _["instrument"] == "HSTDM" else 1
                 )
+        except KeyError:
+            print(f"`n_epec_frame` is not found in {_}")
+            raise KeyError(f"`n_epec_frame` is not found in {_}")
         plan_basis = extract_basis_table(
             qr.data,
             PLAN_BASIS_KEYS,