diff --git a/plugins/ui/src/deephaven/ui/_internal/utils.py b/plugins/ui/src/deephaven/ui/_internal/utils.py
index f31d57a6e..33048a053 100644
--- a/plugins/ui/src/deephaven/ui/_internal/utils.py
+++ b/plugins/ui/src/deephaven/ui/_internal/utils.py
@@ -37,6 +37,19 @@
 }
 
 
+def is_nullish(value: Any) -> bool:
+    """
+    Check if a value is None or Undefined.
+
+    Args:
+        value: The value to check.
+
+    Returns:
+        Whether the value is nullish.
+    """
+    return value is None or value is UNDEFINED
+
+
 def get_component_name(component: Any) -> str:
     """
     Get the name of the component
@@ -639,11 +652,11 @@ def convert_date_props(
         The converted props.
     """
     for key in simple_date_props:
-        if props.get(key) is not UNDEFINED:
+        if not is_nullish(props.get(key)):
             props[key] = _convert_to_java_date(props[key])
 
     for key in date_range_props:
-        if props.get(key) is not UNDEFINED:
+        if not is_nullish(props.get(key)):
             props[key] = convert_date_range(props[key], _convert_to_java_date)
 
     # the simple props must be converted before this to simplify the callable conversion
@@ -660,18 +673,18 @@ def convert_date_props(
 
     # now that the converter is set, we can convert simple props to strings
     for key in simple_date_props:
-        if props.get(key) is not UNDEFINED:
+        if not is_nullish(props.get(key)):
             props[key] = str(props[key])
 
     # and convert the date range props to strings
     for key in date_range_props:
-        if props.get(key) is not UNDEFINED:
+        if not is_nullish(props.get(key)):
             props[key] = convert_date_range(props[key], str)
 
     # wrap the date callable with the convert
     # if there are date range props, we need to convert as a date range
     for key in callable_date_props:
-        if props.get(key) is not UNDEFINED:
+        if not is_nullish(props.get(key)):
             if not callable(props[key]):
                 raise TypeError(f"{key} must be a callable")
             if len(date_range_props) > 0:
@@ -703,7 +716,7 @@ def convert_time_props(
         The converted props.
     """
     for key in simple_time_props:
-        if props.get(key) is not None:
+        if not is_nullish(props.get(key)):
             props[key] = _convert_to_java_time(props[key])
 
     # the simple props must be converted before this to simplify the callable conversion
@@ -711,12 +724,12 @@ def convert_time_props(
 
     # now that the converter is set, we can convert simple props to strings
     for key in simple_time_props:
-        if props.get(key) is not None:
+        if not is_nullish(props.get(key)):
             props[key] = str(props[key])
 
     # wrap the date callable with the convert
     for key in callable_time_props:
-        if props.get(key) is not None:
+        if not is_nullish(props.get(key)):
             if not callable(props[key]):
                 raise TypeError(f"{key} must be a callable")
             props[key] = _wrap_time_callable(props[key], converter)
diff --git a/plugins/ui/src/deephaven/ui/components/stack.py b/plugins/ui/src/deephaven/ui/components/stack.py
index 3a2745c21..bc7556bae 100644
--- a/plugins/ui/src/deephaven/ui/components/stack.py
+++ b/plugins/ui/src/deephaven/ui/components/stack.py
@@ -10,7 +10,7 @@ def stack(
     *children: Any,
     height: float | Undefined = UNDEFINED,
     width: float | Undefined = UNDEFINED,
-    activeItemIndex: int | Undefined = UNDEFINED,
+    active_item_index: int | Undefined = UNDEFINED,
     key: str | Undefined = UNDEFINED,
     **kwargs: Any,
 ) -> Element: