diff --git a/dggrid4py/dggrid_runner.py b/dggrid4py/dggrid_runner.py
index b3f1c80..b45b068 100644
--- a/dggrid4py/dggrid_runner.py
+++ b/dggrid4py/dggrid_runner.py
@@ -988,7 +988,8 @@ def dgapi_grid_transform(
         subset_conf.update(input_extras)
         if subset_conf:
             for elem, value in subset_conf.items():
-                metafile.append(f"{elem} " + str(value))
+                if (value is not None):
+                    metafile.append(f"{elem} " + str(value))
 
         # transform output_types
         output_conf = {}