init _guids

Author: tomvanmele

CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * Fixed bug in `Pointcloud.from_box()`.
 * Changed `compas.scene.MeshObject` to not use vertex coordinate caching because it is too fragile.
 * Changed `compas_rhino.scene.RhinoMeshObject` to keep track of element-guid pairs in dicts.
+* Changed `compas.scene.Scene._guids` to a default value of `[]`.
 
 ### Removed
 

src/compas/scene/sceneobject.py

@@ -111,7 +111,7 @@ def __init__(
         # which means that adding child objects will be added in context "None"
         self.context = context
         self._item = item
-        self._guids = None
+        self._guids = []
         self._node = None
         self._frame = frame
         self._transformation = transformation