diff --git a/python/cugraph-service/server/cugraph_service_server/cugraph_handler.py b/python/cugraph-service/server/cugraph_service_server/cugraph_handler.py
index 6cdf0d793d4..f60f597cfae 100644
--- a/python/cugraph-service/server/cugraph_service_server/cugraph_handler.py
+++ b/python/cugraph-service/server/cugraph_service_server/cugraph_handler.py
@@ -1,4 +1,4 @@
-# Copyright (c) 2022-2023, NVIDIA CORPORATION.
+# Copyright (c) 2022-2024, NVIDIA CORPORATION.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -1370,7 +1370,23 @@ def __get_graph_data_as_numpy_bytes(self, dataframe, null_replacement_value):
             # FIXME: should something other than a numpy type be serialized to
             # prevent a copy? (note: any other type required to be de-serialzed
             # on the client end could add dependencies on the client)
-            df_numpy = dataframe.to_numpy(na_value=n)
+            df_copy = dataframe.copy()
+            for col_name in df_copy.columns:
+                if df_copy[col_name].dtype == "category":
+                    cat_dt = df_copy.dtypes[col_name].categories.dtype
+                    if cat_dt == "object":
+                        new_cat = str(n)
+                    else:
+                        new_cat = n
+                    if new_cat not in df_copy.dtypes[col_name].categories:
+                        df_copy[col_name] = df_copy[col_name].cat.add_categories(
+                            new_cat
+                        )
+                    df_copy[col_name].fillna(new_cat, inplace=True)
+                else:
+                    df_copy[col_name].fillna(n, inplace=True)
+
+            df_numpy = df_copy.to_numpy()
             return df_numpy.dumps()
 
         except Exception:
diff --git a/python/cugraph-service/server/cugraph_service_server/testing/benchmark_server_extension.py b/python/cugraph-service/server/cugraph_service_server/testing/benchmark_server_extension.py
index 361226c8071..dbd75e6abd9 100644
--- a/python/cugraph-service/server/cugraph_service_server/testing/benchmark_server_extension.py
+++ b/python/cugraph-service/server/cugraph_service_server/testing/benchmark_server_extension.py
@@ -1,4 +1,4 @@
-# Copyright (c) 2022-2023, NVIDIA CORPORATION.
+# Copyright (c) 2022-2024, NVIDIA CORPORATION.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -25,12 +25,12 @@
 def create_graph_from_builtin_dataset(dataset_name, mg=False, server=None):
     dataset_obj = getattr(datasets, dataset_name)
     # FIXME: create an MG graph if server is mg?
-    return dataset_obj.get_graph(fetch=True)
+    return dataset_obj.get_graph(download=True)
 
 
 def create_property_graph_from_builtin_dataset(dataset_name, mg=False, server=None):
     dataset_obj = getattr(datasets, dataset_name)
-    edgelist_df = dataset_obj.get_edgelist(fetch=True)
+    edgelist_df = dataset_obj.get_edgelist(download=True)
 
     if mg and (server is not None) and server.is_multi_gpu:
         G = MGPropertyGraph()
diff --git a/python/cugraph/cugraph/structure/property_graph.py b/python/cugraph/cugraph/structure/property_graph.py
index 513798f35f9..53c1bf778c7 100644
--- a/python/cugraph/cugraph/structure/property_graph.py
+++ b/python/cugraph/cugraph/structure/property_graph.py
@@ -1,4 +1,4 @@
-# Copyright (c) 2021-2023, NVIDIA CORPORATION.
+# Copyright (c) 2021-2024, NVIDIA CORPORATION.
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
@@ -123,6 +123,17 @@ class EXPERIMENTAL__PropertyGraph:
 
     _default_type_name = ""
 
+    _internal_col_names = set(
+        (
+            vertex_col_name,
+            src_col_name,
+            dst_col_name,
+            type_col_name,
+            edge_id_col_name,
+            weight_col_name,
+        )
+    )
+
     def __init__(self):
         # The dataframe containing the properties for each vertex.
         # Each vertex occupies a row, and individual properties are maintained
@@ -1380,6 +1391,15 @@ def fillna_vertices(self, val=0):
             Series is passed, the index or keys are the columns to fill
             and the values are the fill value for the corresponding column.
         """
+        # Omit internal columns if an object is passed in to be applied to the
+        # entire DataFrame and assume the intent is for users to fillna only on
+        # their data.
+        if type(val) not in [dict, self.__series_type]:
+            user_col_names = (
+                set(self.__vertex_prop_dataframe.columns) - self._internal_col_names
+            )
+            val = dict((k, val) for k in user_col_names)
+
         self.__vertex_prop_dataframe.fillna(val, inplace=True)
 
     def fillna_edges(self, val=0):
@@ -1394,6 +1414,14 @@ def fillna_edges(self, val=0):
             Series is passed, the index or keys are the columns to fill
             and the values are the fill value for the corresponding column.
         """
+        # Omit internal columns if an object is passed in to be applied to the
+        # entire DataFrame and assume the intent is for users to fillna only on
+        # their data.
+        if type(val) not in [dict, self.__series_type]:
+            user_col_names = (
+                set(self.__edge_prop_dataframe.columns) - self._internal_col_names
+            )
+            val = dict((k, val) for k in user_col_names)
 
         self.__edge_prop_dataframe.fillna(val, inplace=True)