Fix serializing optional Collection attributes

CHANGELOG.md

@@ -16,6 +16,7 @@
 ### Fixed
 
 - Dependency resolution when installing `requirements-dev.txt` ([#897](https://github.com/stac-utils/pystac/pull/897))
+- Serializing optional Collection attributes ([#916](https://github.com/stac-utils/pystac/pull/916))
 
 ## [v1.6.1]
 

pystac/catalog.py

@@ -510,7 +510,7 @@ def to_dict(
             "links": [link.to_dict(transform_href=transform_hrefs) for link in links],
         }
 
-        if self.stac_extensions is not None:
+        if self.stac_extensions:
             d["stac_extensions"] = self.stac_extensions
 
         for key in self.extra_fields:

pystac/collection.py

@@ -559,11 +559,11 @@ def to_dict(
         )
         d["extent"] = self.extent.to_dict()
         d["license"] = self.license
-        if self.stac_extensions is not None:
+        if self.stac_extensions:
             d["stac_extensions"] = self.stac_extensions
-        if self.keywords is not None:
+        if self.keywords:
             d["keywords"] = self.keywords
-        if self.providers is not None:
+        if self.providers:
             d["providers"] = list(map(lambda x: x.to_dict(), self.providers))
         if not self.summaries.is_empty():
             d["summaries"] = self.summaries.to_dict()
@@ -629,19 +629,19 @@ def from_dict(
         description = d.pop("description")
         license = d.pop("license")
         extent = Extent.from_dict(d.pop("extent"))
-        title = d.get("title")
-        stac_extensions = d.get("stac_extensions")
-        keywords = d.get("keywords")
-        providers = d.get("providers")
+        title = d.pop("title", None)
+        stac_extensions = d.pop("stac_extensions", None)
+        keywords = d.pop("keywords", None)
+        providers = d.pop("providers", None)
         if providers is not None:
             providers = list(map(lambda x: pystac.Provider.from_dict(x), providers))
-        summaries = d.get("summaries")
+        summaries = d.pop("summaries", None)
         if summaries is not None:
             summaries = Summaries(summaries)
 
-        assets: Optional[Dict[str, Any]] = {
-            k: Asset.from_dict(v) for k, v in d.get("assets", {}).items()
-        }
+        assets = d.pop("assets", None)
+        if assets:
+            assets = {k: Asset.from_dict(v) for k, v in assets.items()}
         links = d.pop("links")
 
         d.pop("stac_version")

tests/test_collection.py

@@ -226,6 +226,43 @@ def test_assets(self) -> None:
         collection = pystac.Collection.from_dict(data)
         collection.validate()
 
+    def test_removing_optional_attributes(self) -> None:
+        path = TestCases.get_path("data-files/collections/with-assets.json")
+        with open(path, "r") as file:
+            data = json.load(file)
+        data["title"] = "dummy title"
+        data["stac_extensions"] = ["dummy extension"]
+        data["keywords"] = ["key", "word"]
+        data["providers"] = [{"name": "pystac"}]
+        collection = pystac.Collection.from_dict(data)
+
+        # Assert we have everything set
+        assert collection.title
+        assert collection.stac_extensions
+        assert collection.keywords
+        assert collection.providers
+        assert collection.summaries
+        assert collection.assets
+
+        # Remove all of the optional stuff
+        collection.title = None
+        collection.stac_extensions = []
+        collection.keywords = []
+        collection.providers = []
+        collection.summaries = pystac.Summaries({})
+        collection.assets = {}
+
+        collection_as_dict = collection.to_dict()
+        for key in (
+            "title",
+            "stac_extensions",
+            "keywords",
+            "providers",
+            "summaries",
+            "assets",
+        ):
+            assert key not in collection_as_dict
+
     def test_from_dict_preserves_dict(self) -> None:
         path = TestCases.get_path("data-files/collections/with-assets.json")
         with open(path) as f: