cleanup and polish

com.unity.perception/Editor/GroundTruth/LabelingEditor.cs

             }
         }
 
+        private bool AreSelectedAssetsCompatibleWithAutoLabelScheme(AssetLabelingScheme scheme)
+        {
+            foreach (var asset in serializedObject.targetObjects)
+            {
+                string label = scheme.GenerateLabel(asset);
+                if (label == null)
+                {
+                    return false;
+                }
+            }
+            return true;
+        }
+
-            m_LabelingSchemes.Add(new AssetNameLabelingScheme());
-            m_LabelingSchemes.Add(new AssetFileNameLabelingScheme());
-            m_LabelingSchemes.Add(new CurrentOrParentsFolderNameLabelingScheme());
+            AssetLabelingScheme labelingScheme = new AssetNameLabelingScheme();
+            if (AreSelectedAssetsCompatibleWithAutoLabelScheme(labelingScheme)) m_LabelingSchemes.Add(labelingScheme);
+
+            labelingScheme = new AssetFileNameLabelingScheme();
+            if (AreSelectedAssetsCompatibleWithAutoLabelScheme(labelingScheme)) m_LabelingSchemes.Add(labelingScheme);
+
+            labelingScheme = new CurrentOrParentsFolderNameLabelingScheme();
+            if (AreSelectedAssetsCompatibleWithAutoLabelScheme(labelingScheme)) m_LabelingSchemes.Add(labelingScheme);
 
             var descriptions = m_LabelingSchemes.Select(scheme => scheme.Description).ToList();
             descriptions.Insert(0, "<Select Scheme>");

com.unity.perception/Runtime/GroundTruth/Labeling/Labeling.cs

         public override string GenerateLabel(Object asset)
         {
             string assetPath = Labeling.GetAssetOrPrefabPath(asset);
-            var stringList = assetPath?.Split(Labeling.PathSeparators, StringSplitOptions.RemoveEmptyEntries)
+            var stringList = assetPath.Split(Labeling.PathSeparators, StringSplitOptions.RemoveEmptyEntries)
-            return stringList?.Last();
+            return stringList.Count > 0 ? stringList.Last() : null;
         }
     }
 
         public override string GenerateLabel(Object asset)
         {
             string assetPath = Labeling.GetAssetOrPrefabPath(asset);
-            var stringList = assetPath?.Split(Labeling.PathSeparators, StringSplitOptions.RemoveEmptyEntries)
+            var stringList = assetPath.Split(Labeling.PathSeparators, StringSplitOptions.RemoveEmptyEntries)
-
-            //if stringList is not null, it always has at least two members, the file's name and the parent folder
-            return stringList?[stringList.Count-2];
+            return stringList.Count > 1 ? stringList[stringList.Count-2] : null;
         }
     }
 }