return empty if input is empty in dispatchers

csst_dag/dag/_dispatcher.py

@@ -263,6 +263,10 @@ class Dispatcher:
         # unique obsid --> useless
         # u_obsid = table.unique(data_basis["dataset", "obs_id"])
 
+        # return an empty list if input is empty
+        if len(plan_basis) == 0 or len(data_basis) == 0:
+            return []
+
         # initialize task list
         task_list = []
 
@@ -338,6 +342,10 @@ class Dispatcher:
             )
             return sum(task_list, [])
 
+        # return an empty list if input is empty
+        if len(plan_basis) == 0 or len(data_basis) == 0:
+            return []
+
         # unique obsid
         u_obsid = table.unique(data_basis["dataset", "obs_id"])
         relevant_plan = table.join(
@@ -450,6 +458,10 @@ class Dispatcher:
             )
             return sum(task_list, [])
 
+        # return an empty list if input is empty
+        if len(plan_basis) == 0 or len(data_basis) == 0:
+            return []
+
         # unique obsid
         u_obsid = table.unique(data_basis["dataset", "obs_id"])
         relevant_plan = table.join(
@@ -562,6 +574,10 @@ class Dispatcher:
         data_basis: table.Table,
         # n_jobs: int = 1,
     ):
+        # return an empty list if input is empty
+        if len(plan_basis) == 0 or len(data_basis) == 0:
+            return []
+
         # unique obsgroup basis (using group_by)
         obsgroup_basis = plan_basis.group_by(
             keys=[
@@ -652,6 +668,10 @@ class Dispatcher:
         # 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 []
+
         # unique obsgroup basis
         obsgroup_basis = table.unique(
             plan_basis[