diff --git a/src/snapwrap/SEEMeta/assembly.py b/src/snapwrap/SEEMeta/assembly.py
index a3f36b9..4a54c10 100644
--- a/src/snapwrap/SEEMeta/assembly.py
+++ b/src/snapwrap/SEEMeta/assembly.py
@@ -60,10 +60,11 @@ class Assembly:
     version: ClassVar[int] = 1
 
     components: List[Component] = field(default_factory=list)
-    comment: Optional[str] = None
-    model: Optional[str] = None
-    serialNumber: Optional[str] = None
+    comment: Optional[str] = "None"
+    model: Optional[str] = "None"
+    serialNumber: Optional[str] = "None"
     orientation: List[float] = field(default_factory=lambda: [0.0, 1.0, 0.0])
+    origin: List[float] = field(default_factory=lambda: [0.0, 0.0, 0.0])
     stringDescriptor: str = field(init=False)
 
     def __post_init__(self) -> None:
@@ -226,4 +227,9 @@ def __post_init__(self) -> None:
                     "CylinderCell: cylinders must be adjoining and concentric; "
                     f"{i}: innerDiameter ({cur.innerDiameter.value}{cur.innerDiameter.units}) "
                     f"!= previous outerDiameter ({prev.outerDiameter.value}{prev.outerDiameter.units})"
-                )
\ No newline at end of file
+                )
+            
+@register_assembly
+@dataclass(slots=True, kw_only=True)
+class empty(Assembly):
+    kind: ClassVar[str] = "assembly.empty"
\ No newline at end of file
diff --git a/src/snapwrap/SEEMeta/component.py b/src/snapwrap/SEEMeta/component.py
index 05ba6c1..67171e8 100644
--- a/src/snapwrap/SEEMeta/component.py
+++ b/src/snapwrap/SEEMeta/component.py
@@ -147,13 +147,13 @@ class Component:
     # Schema version for this specific kind
     version: ClassVar[int] = 1
 
-    manufacturer: Optional[str] = None
-    model: Optional[str] = None
-    serialNumber: Optional[str] = None
-    location: Optional[str] = None
+    manufacturer: Optional[str] = "None"
+    model: Optional[str] = "None"
+    serialNumber: Optional[str] = "None"
+    location: Optional[str] = "None"
     # Optional human-readable description
-    comment: Optional[str] = None
-    stlFile: Optional[str] = None
+    comment: Optional[str] = "None"
+    stlFile: Optional[str] = "None"
 
     # ---- Serialization ----
     def to_dict(self) -> Dict[str, Any]:
@@ -472,7 +472,7 @@ def __post_init__(self):
         # derived descriptor (include model/serial if available)
         model = getattr(self, "model", None) or "unknown"
         sn = getattr(self, "serialNumber", None)
-        self.stringDescriptor = f"aux_{model}" + (f"_{sn}" if sn else "")
+        self.stringDescriptor = f"aux_{self.manufacturer}" + (f"_{sn}" if sn else "")
         self.stlFile = f"{self.stringDescriptor}.stl"
 
 @register