diff --git a/fre/make/tests/compilation/test_run_fremake_builds.py b/fre/make/tests/compilation/test_run_fremake_builds.py
index 1be4731c..3967323a 100644
--- a/fre/make/tests/compilation/test_run_fremake_builds.py
+++ b/fre/make/tests/compilation/test_run_fremake_builds.py
@@ -1,6 +1,6 @@
-''' this file holds any run-fremake tests that actually compile the model code'''
-''' these tests assume your os is the ci image (gcc 14 + mpich on rocky 8)'''
-''' you may need to add mkmf to your path or make other adjustments to the mkmf template to run elsewhere'''
+''' this file holds any run-fremake tests that actually compile the model code
+ these tests assume your os is the ci image (gcc 14 + mpich on rocky 8)
+ you may need to add mkmf to your path or make other adjustments to the mkmf template to run elsewhere'''
 
 import os
 from shutil  import rmtree
diff --git a/fre/pp/run_script.py b/fre/pp/run_script.py
index a5d7d54d..0865ff10 100644
--- a/fre/pp/run_script.py
+++ b/fre/pp/run_script.py
@@ -2,11 +2,15 @@
 
 import subprocess
 
-def pp_run_subtool(experiment, platform, target):
+def pp_run_subtool(experiment = None, platform = None, target = None):
     """
     Start or restart the Cylc workflow identified by:
     <experiment>__<platform>__<target>
     """
+    if None in [experiment, platform, target]:
+        raise ValueError( 'experiment, platform, and target must all not be None.'
+                          'currently, their values are...'
+                          f'{experiment} / {platform} / {target}')
 
     name = experiment + '__' + platform + '__' + target
     cmd = f"cylc play {name}"