Store the NaN fill value used by the original NaNCleaner

model2/preprocessor_config.json

@@ -691,9 +691,9 @@
     "year_progress_cos": -0.004568948580583765,
     "year_progress_sin": 0.0006449962704664358
   },
-  "nan_filled_variables": [
-    "sea_surface_temperature"
-  ],
+  "nan_fill_values": {
+    "sea_surface_temperature": 269.48291015625
+  },
   "num_input_timesteps": 2,
   "pressure_levels": [
     50,
@@ -1080,4 +1080,4 @@
     "cyclone_usa_pres_disc"
   ],
   "time_step_hours": 6
-}
+}