diff --git a/notion_client/helpers.py b/notion_client/helpers.py
index 0953bcb..222aeea 100644
--- a/notion_client/helpers.py
+++ b/notion_client/helpers.py
@@ -3,59 +3,13 @@
 from urllib.parse import urlparse
 from uuid import UUID
 
-NOT_NULLABLE = (
-    "after",
-    "ai_block",
-    "archived",
-    "audio",
-    "bookmark",
-    "breadcrumb",
-    "bulleted_list_item",
-    "callout",
-    "code",
-    "description",
-    "discussion_id",
-    "divider",
-    "embed",
-    "equation",
-    "file",
-    "filter",
-    "heading_1",
-    "heading_2",
-    "heading_3",
-    "image",
-    "is_inline",
-    "link_to_page",
-    "numbered_list_item",
-    "page_size",
-    "pdf",
-    "properties",
-    "query",
-    "quote",
-    "sort",
-    "sorts",
-    "start_cursor",
-    "synced_block",
-    "table",
-    "table_of_contents",
-    "table_row",
-    "template",
-    "title",
-    "to_do",
-    "toggle",
-    "type",
-    "video",
-)
-
 
 def pick(base: Dict[Any, Any], *keys: str) -> Dict[Any, Any]:
     """Return a dict composed of key value pairs for keys passed as args."""
     result = {}
     for key in keys:
-        value = base.get(key)
-        if value is None and key in NOT_NULLABLE:
-            continue
-        result[key] = value
+        if key in base and key != "start_cursor":
+            result[key] = base.get(key)
     return result
 
 
@@ -83,7 +37,10 @@ def iterate_paginated_api(
     next_cursor = kwargs.pop("start_cursor", None)
 
     while True:
-        response = function(**kwargs, start_cursor=next_cursor)
+        if next_cursor:
+            kwargs["start_cursor"] = next_cursor
+
+        response = function(**kwargs)
         yield response.get("results")
 
         next_cursor = response.get("next_cursor")
@@ -106,7 +63,10 @@ async def async_iterate_paginated_api(
     next_cursor = kwargs.pop("start_cursor", None)
 
     while True:
-        response = await function(**kwargs, start_cursor=next_cursor)
+        if next_cursor:
+            kwargs["start_cursor"] = next_cursor
+
+        response = await function(**kwargs)
         yield response.get("results")
 
         next_cursor = response.get("next_cursor")