Fixup: gen_data can't be none

as every everest config must have
controls which turn into gendata

src/ert/simulator/batch_simulator.py

@@ -102,24 +102,15 @@ def callback(*args, **kwargs):
                 )
             )
 
-        if "gen_data" not in ens_config:
-            ens_config.addNode(
-                GenDataConfig(
-                    keys=results,
-                    input_files=[f"{k}_%d" for k in results],
-                    report_steps_list=[[0] for _ in results],
-                )
-            )
-        else:
-            existing_gendata = ens_config.response_configs["gen_data"]
-            existing_keys = existing_gendata.keys
-            assert isinstance(existing_gendata, GenDataConfig)
-
-            for key in results:
-                if key not in existing_keys:
-                    existing_gendata.keys.append(key)
-                    existing_gendata.input_files.append(f"{key}_%d")
-                    existing_gendata.report_steps_list.append([0])
+        existing_gendata = ens_config.response_configs["gen_data"]
+        existing_keys = existing_gendata.keys
+        assert isinstance(existing_gendata, GenDataConfig)
+
+        for key in results:
+            if key not in existing_keys:
+                existing_gendata.keys.append(key)
+                existing_gendata.input_files.append(f"{key}_%d")
+                existing_gendata.report_steps_list.append([0])
 
     def _setup_sim(
         self,