unit: null now gives [-] as the unit

Author: joehart2001

ml_peg/analysis/surfaces/OC157/metrics.yml

@@ -8,6 +8,6 @@ metrics:
   Ranking Error:
     good: 0.0
     bad: 1.0
-    unit: "-"
+    unit: null
     tooltip: Error in ranking stability across triplets
     level_of_theory: PBE

ml_peg/analysis/utils/utils.py

@@ -57,7 +57,10 @@ def load_metrics_config(config_path: Path) -> tuple[Thresholds, dict[str, str]]:
                 f"Metric '{metric_name}' must define a 'unit' entry in {config_path}"
             )
 
-        unit_value = str(metric_config["unit"]).strip()
+        if unit_value := metric_config["unit"] is not None:
+            unit_value = str(metric_config["unit"]).strip()
+        else:
+            unit_value = "-"
 
         metric_threshold: ThresholdEntry = {
             "good": good_value,