FIX: set default propertiers Field

Author: genematx

tiled/stream_messages.py

@@ -25,7 +25,7 @@ class DataSource(BaseModel, Generic[StructureT]):
     structure: StructureT
     mimetype: str
     parameters: dict
-    properties: Optional[dict]
+    properties: dict = Field(default_factory=dict) # TODO: make this required in a future release. See Issue #1300
     assets: list[Asset]
     management: Management