diff --git a/hw/dv/data/common_sim_cfg.hjson b/hw/dv/data/common_sim_cfg.hjson
index c3b4614..48a4286 100644
--- a/hw/dv/data/common_sim_cfg.hjson
+++ b/hw/dv/data/common_sim_cfg.hjson
@@ -112,23 +112,21 @@
   regressions: [
     {
       name: sanity
+      tests: []
       reseed: 1
     }
 
     {
       name: all
-      tests: []
     }
 
     {
       name: all_once
       reseed: 1
-      tests: []
     }
 
     {
       name: nightly
-      tests: []
       en_sim_modes: ["cov"]
     }
   ]
diff --git a/util/dvsim/Modes.py b/util/dvsim/Modes.py
index ac6ef6d..bf0243d 100644
--- a/util/dvsim/Modes.py
+++ b/util/dvsim/Modes.py
@@ -84,7 +84,7 @@
             self_attr_val = getattr(self, attr)
             mode_attr_val = getattr(mode, attr)
 
-            if type(self_attr_val) is list:
+            if type(self_attr_val) is list and type(mode_attr_val) is list:
                 self_attr_val.extend(mode_attr_val)
                 setattr(self, attr, self_attr_val)
 
@@ -422,7 +422,7 @@
         self.type = ""
         if not hasattr(self, "mname"):
             self.mname = "regression"
-        self.tests = []
+        self.tests = None
         self.reseed = None
         self.test_names = []
         self.excl_tests = []  # TODO: add support for this
@@ -520,7 +520,7 @@
                 regression_obj.run_opts.extend(run_mode_obj.run_opts)
 
             # Unpack tests
-            if regression_obj.tests == []:
+            if regression_obj.tests is None:
                 log.log(VERBOSE,
                         "Unpacking all tests in scope for regression \"%s\"",
                         regression_obj.name)