fix: clear cba_series_id, default_playlist_id

Closes #178

program/serializers.py

@@ -495,6 +495,8 @@ class ShowSerializer(serializers.HyperlinkedModelSerializer):
     category_ids = serializers.PrimaryKeyRelatedField(
         many=True, queryset=Category.objects.all(), source="category"
     )
+    cba_series_id = serializers.IntegerField(allow_null=True)
+    default_playlist_id = serializers.IntegerField(allow_null=True)
     funding_category_id = serializers.PrimaryKeyRelatedField(
         queryset=FundingCategory.objects.all(), source="funding_category"
     )
@@ -559,15 +561,14 @@ class ShowSerializer(serializers.HyperlinkedModelSerializer):
             "type_id",
         ) + read_only_fields
 
-    @staticmethod
-    def validate_cba_series_id(value):
-        # FIXME: ugly hack to capture 0 as None
-        return None if value == 0 else value
+    def to_internal_value(self, data):
+        if data.get("cba_series_id") == "":
+            data["cba_series_id"] = None
 
-    @staticmethod
-    def validate_default_playlist_id(value):
-        # FIXME: ugly hack to capture 0 as None
-        return None if value == 0 else value
+        if data.get("default_playlist_id") == "":
+            data["default_playlist_id"] = None
+
+        return super().to_internal_value(data)
 
     def create(self, validated_data):
         """