Enable rich_text_* elements to have an empty 'elements' property

slack_sdk/models/basic_objects.py

@@ -12,6 +12,15 @@ def __str__(self):
         return f"<slack_sdk.{self.__class__.__name__}>"
 
 
+# Usually, Block Kit components do not allow an empty array for a property value, but there are some exceptions.
+EMPTY_ALLOWED_TYPE_AND_PROPERTY_LIST = [
+    {"type": "rich_text_section", "property": "elements"},
+    {"type": "rich_text_list", "property": "elements"},
+    {"type": "rich_text_preformatted", "property": "elements"},
+    {"type": "rich_text_quote", "property": "elements"},
+]
+
+
 class JsonObject(BaseObject, metaclass=ABCMeta):
     """The base class for JSON serializable class objects"""
 
@@ -51,6 +60,14 @@ def is_not_empty(self, key: str) -> bool:
             value = getattr(self, key, None)
             if value is None:
                 return False
+
+            # Usually, Block Kit components do not allow an empty array for a property value, but there are some exceptions.
+            # The following code deals with these exceptions:
+            type_value = getattr(self, "type", None)
+            for empty_allowed in EMPTY_ALLOWED_TYPE_AND_PROPERTY_LIST:
+                if type_value == empty_allowed["type"] and key == empty_allowed["property"]:
+                    return True
+
             has_len = getattr(value, "__len__", None) is not None
             if has_len:  # skipcq: PYL-R1705
                 return len(value) > 0

tests/slack_sdk/models/test_blocks.py

@@ -1143,3 +1143,27 @@ def test_elements_are_parsed(self):
         self.assertIsInstance(block.elements[3], RichTextListElement)
         self.assertIsInstance(block.elements[3].elements[0], RichTextSectionElement)
         self.assertIsInstance(block.elements[3].elements[0].elements[0], RichTextElementParts.Text)
+
+    def test_parsing_empty_block_elements(self):
+        empty_element_block = {
+            "block_id": "my-block",
+            "type": "rich_text",
+            "elements": [
+                {"type": "rich_text_section", "elements": []},
+                {"type": "rich_text_list", "style": "bullet", "elements": []},
+                {"type": "rich_text_preformatted", "elements": []},
+                {"type": "rich_text_quote", "elements": []},
+            ],
+        }
+        block = RichTextBlock(**empty_element_block)
+        self.assertIsInstance(block.elements[0], RichTextSectionElement)
+        self.assertIsNotNone(block.elements[0].elements)
+        self.assertIsNotNone(block.elements[1].elements)
+        self.assertIsNotNone(block.elements[2].elements)
+        self.assertIsNotNone(block.elements[3].elements)
+
+        block_dict = block.to_dict()
+        self.assertIsNotNone(block_dict["elements"][0].get("elements"))
+        self.assertIsNotNone(block_dict["elements"][1].get("elements"))
+        self.assertIsNotNone(block_dict["elements"][2].get("elements"))
+        self.assertIsNotNone(block_dict["elements"][3].get("elements"))