diff --git a/a2a_agents/python/a2ui_agent/src/a2ui/extension/a2ui_extension.py b/a2a_agents/python/a2ui_agent/src/a2ui/extension/a2ui_extension.py
index 150607b92..c8155d49e 100644
--- a/a2a_agents/python/a2ui_agent/src/a2ui/extension/a2ui_extension.py
+++ b/a2a_agents/python/a2ui_agent/src/a2ui/extension/a2ui_extension.py
@@ -89,7 +89,7 @@ def get_a2ui_datapart(part: Part) -> Optional[DataPart]:
 
 def get_a2ui_agent_extension(
     accepts_inline_catalogs: bool = False,
-    supported_catalog_ids: List[str] = [],
+    supported_catalog_ids: Optional[List[str]] = None,
 ) -> AgentExtension:
   """Creates the A2UI AgentExtension configuration.
 
@@ -100,6 +100,8 @@ def get_a2ui_agent_extension(
   Returns:
       The configured A2UI AgentExtension.
   """
+  if supported_catalog_ids is None:
+    supported_catalog_ids = []
   params = {}
   if accepts_inline_catalogs:
     params[AGENT_EXTENSION_ACCEPTS_INLINE_CATALOGS_KEY] = (
diff --git a/a2a_agents/python/a2ui_agent/src/a2ui/extension/send_a2ui_to_client_toolset.py b/a2a_agents/python/a2ui_agent/src/a2ui/extension/send_a2ui_to_client_toolset.py
index baba339f4..d65906b36 100644
--- a/a2a_agents/python/a2ui_agent/src/a2ui/extension/send_a2ui_to_client_toolset.py
+++ b/a2a_agents/python/a2ui_agent/src/a2ui/extension/send_a2ui_to_client_toolset.py
@@ -311,8 +311,8 @@ def convert_send_a2ui_to_client_genai_part_to_a2a_part(
       return []
 
     final_parts = []
+    logger.info(f"Found {len(json_data)} messages. Creating individual DataParts.")
     for message in json_data:
-      logger.info(f"Found {len(json_data)} messages. Creating individual DataParts.")
       final_parts.append(create_a2ui_part(message))
 
     return final_parts
diff --git a/a2a_agents/python/a2ui_agent/src/a2ui/inference/schema/validator.py b/a2a_agents/python/a2ui_agent/src/a2ui/inference/schema/validator.py
index a42b2052e..2074d9db0 100644
--- a/a2a_agents/python/a2ui_agent/src/a2ui/inference/schema/validator.py
+++ b/a2a_agents/python/a2ui_agent/src/a2ui/inference/schema/validator.py
@@ -130,10 +130,10 @@ def _build_0_9_validator(self) -> Draft202012Validator:
     # these resolve to https://a2ui.org/specification/v0_9/catalog.json.
     # We must register them using these absolute URIs.
     base_uri = self._catalog.s2c_schema.get("$id", BASE_SCHEMA_URL)
-    import os
+    from urllib.parse import urljoin
 
     def get_sibling_uri(uri, filename):
-      return os.path.join(os.path.dirname(uri), filename)
+      return urljoin(uri, filename)
 
     catalog_uri = get_sibling_uri(base_uri, "catalog.json")
     common_types_uri = get_sibling_uri(base_uri, "common_types.json")
diff --git a/renderers/lit/src/0.8/ui/root.ts b/renderers/lit/src/0.8/ui/root.ts
index fcd33df1e..f2188eb5d 100644
--- a/renderers/lit/src/0.8/ui/root.ts
+++ b/renderers/lit/src/0.8/ui/root.ts
@@ -298,7 +298,7 @@ export class Root extends SignalWatcher(LitElement) {
             .surfaceId=${this.surfaceId}
             .dataContextPath=${node.dataContextPath ?? ""}
             .action=${node.properties.action}
-            .childComponents=${[node.properties.child]}
+            .childComponents=${node.properties.child ? [node.properties.child] : []}
             .enableCustomElements=${this.enableCustomElements}
           ></a2ui-button>`;
         }
diff --git a/samples/agent/adk/contact_lookup/agent.py b/samples/agent/adk/contact_lookup/agent.py
index 0bde787c1..cd1b91714 100644
--- a/samples/agent/adk/contact_lookup/agent.py
+++ b/samples/agent/adk/contact_lookup/agent.py
@@ -61,7 +61,7 @@ def __init__(self, base_url: str, use_ui: bool = False):
   def get_agent_card(self) -> AgentCard:
     capabilities = AgentCapabilities(
         streaming=True,
-        extensions=[self._schema_manager.get_agent_extension()],
+        extensions=[self._schema_manager.get_agent_extension()] if self._schema_manager else [],
     )
     skill = AgentSkill(
         id="find_contact",
@@ -196,7 +196,7 @@ async def stream(self, query, session_id) -> AsyncIterable[dict[str, Any]]:
         )
         if attempt <= max_retries:
           current_query_text = (
-              "I received no response. Please try again."
+              "I received no response. Please try again. "
               f"Please retry the original request: '{query}'"
           )
           continue  # Go to next retry