fix(civil3d): uses basecurves as display value when no display value exists

Converters/Civil3d/Speckle.Converters.Civil3dShared/Helpers/DisplayValueExtractor.cs

@@ -31,7 +31,7 @@ IConverterSettingsStore<Civil3dConversionSettings> converterSettings
     _converterSettings = converterSettings;
   }
 
-  public List<Base> GetDisplayValue(CDB.Entity entity)
+  public List<Base>? GetDisplayValue(CDB.Entity entity)
   {
     switch (entity)
     {
@@ -56,7 +56,7 @@ public List<Base> GetDisplayValue(CDB.Entity entity)
         return new() { gridSurfaceMesh };
 
       default:
-        return new();
+        return null;
     }
   }
 }

Converters/Civil3d/Speckle.Converters.Civil3dShared/ToSpeckle/BuiltElements/CivilEntityToSpeckleTopLevelConverter.cs

@@ -59,9 +59,10 @@ public Base Convert(CDB.Entity target)
       civilObject["baseCurves"] = baseCurves;
     }
 
-    // extract display value
-    List<Base> display = _displayValueExtractor.GetDisplayValue(target);
-    if (display.Count > 0)
+    // extract display value.
+    // If object has no display but has basecurves, use basecurves for display instead (for viewer selection)
+    List<Base>? display = _displayValueExtractor.GetDisplayValue(target) ?? baseCurves?.Select(o => (Base)o).ToList();
+    if (display is not null)
     {
       civilObject["displayValue"] = display;
     }

Converters/Civil3d/Speckle.Converters.Civil3dShared/ToSpeckle/Properties/GeneralPropertiesExtractor.cs

@@ -292,7 +292,7 @@ CDB.FeatureLineCollection featurelineCollection in offsetFeaturelineCollection.F
       };
       speedsCount++;
     }
-    designCriteriaDict["Design Speeds"] = designSpeedsDict;
+
     if (designSpeedsDict.Count > 0)
     {
       designCriteriaDict["Design Speeds"] = designSpeedsDict;