diff --git a/pandas/core/frame.py b/pandas/core/frame.py
index 045776c3f5c50..37fc5de95b3d2 100644
--- a/pandas/core/frame.py
+++ b/pandas/core/frame.py
@@ -5007,6 +5007,121 @@ def rename(
             errors=errors,
         )
 
+    @overload
+    def fillna(
+        self,
+        value=...,
+        method: str | None = ...,
+        axis: Axis | None = ...,
+        inplace: Literal[False] = ...,
+        limit=...,
+        downcast=...,
+    ) -> DataFrame:
+        ...
+
+    @overload
+    def fillna(
+        self,
+        value,
+        method: str | None,
+        axis: Axis | None,
+        inplace: Literal[True],
+        limit=...,
+        downcast=...,
+    ) -> None:
+        ...
+
+    @overload
+    def fillna(
+        self,
+        *,
+        inplace: Literal[True],
+        limit=...,
+        downcast=...,
+    ) -> None:
+        ...
+
+    @overload
+    def fillna(
+        self,
+        value,
+        *,
+        inplace: Literal[True],
+        limit=...,
+        downcast=...,
+    ) -> None:
+        ...
+
+    @overload
+    def fillna(
+        self,
+        *,
+        method: str | None,
+        inplace: Literal[True],
+        limit=...,
+        downcast=...,
+    ) -> None:
+        ...
+
+    @overload
+    def fillna(
+        self,
+        *,
+        axis: Axis | None,
+        inplace: Literal[True],
+        limit=...,
+        downcast=...,
+    ) -> None:
+        ...
+
+    @overload
+    def fillna(
+        self,
+        *,
+        method: str | None,
+        axis: Axis | None,
+        inplace: Literal[True],
+        limit=...,
+        downcast=...,
+    ) -> None:
+        ...
+
+    @overload
+    def fillna(
+        self,
+        value,
+        *,
+        axis: Axis | None,
+        inplace: Literal[True],
+        limit=...,
+        downcast=...,
+    ) -> None:
+        ...
+
+    @overload
+    def fillna(
+        self,
+        value,
+        method: str | None,
+        *,
+        inplace: Literal[True],
+        limit=...,
+        downcast=...,
+    ) -> None:
+        ...
+
+    @overload
+    def fillna(
+        self,
+        value=...,
+        method: str | None = ...,
+        axis: Axis | None = ...,
+        inplace: bool = ...,
+        limit=...,
+        downcast=...,
+    ) -> DataFrame | None:
+        ...
+
     @doc(NDFrame.fillna, **_shared_doc_kwargs)
     def fillna(
         self,
diff --git a/pandas/core/series.py b/pandas/core/series.py
index 4b36b846ef9c4..5c605a6b441c6 100644
--- a/pandas/core/series.py
+++ b/pandas/core/series.py
@@ -4581,6 +4581,121 @@ def drop(
             errors=errors,
         )
 
+    @overload
+    def fillna(
+        self,
+        value=...,
+        method: str | None = ...,
+        axis: Axis | None = ...,
+        inplace: Literal[False] = ...,
+        limit=...,
+        downcast=...,
+    ) -> Series:
+        ...
+
+    @overload
+    def fillna(
+        self,
+        value,
+        method: str | None,
+        axis: Axis | None,
+        inplace: Literal[True],
+        limit=...,
+        downcast=...,
+    ) -> None:
+        ...
+
+    @overload
+    def fillna(
+        self,
+        *,
+        inplace: Literal[True],
+        limit=...,
+        downcast=...,
+    ) -> None:
+        ...
+
+    @overload
+    def fillna(
+        self,
+        value,
+        *,
+        inplace: Literal[True],
+        limit=...,
+        downcast=...,
+    ) -> None:
+        ...
+
+    @overload
+    def fillna(
+        self,
+        *,
+        method: str | None,
+        inplace: Literal[True],
+        limit=...,
+        downcast=...,
+    ) -> None:
+        ...
+
+    @overload
+    def fillna(
+        self,
+        *,
+        axis: Axis | None,
+        inplace: Literal[True],
+        limit=...,
+        downcast=...,
+    ) -> None:
+        ...
+
+    @overload
+    def fillna(
+        self,
+        *,
+        method: str | None,
+        axis: Axis | None,
+        inplace: Literal[True],
+        limit=...,
+        downcast=...,
+    ) -> None:
+        ...
+
+    @overload
+    def fillna(
+        self,
+        value,
+        *,
+        axis: Axis | None,
+        inplace: Literal[True],
+        limit=...,
+        downcast=...,
+    ) -> None:
+        ...
+
+    @overload
+    def fillna(
+        self,
+        value,
+        method: str | None,
+        *,
+        inplace: Literal[True],
+        limit=...,
+        downcast=...,
+    ) -> None:
+        ...
+
+    @overload
+    def fillna(
+        self,
+        value=...,
+        method: str | None = ...,
+        axis: Axis | None = ...,
+        inplace: bool = ...,
+        limit=...,
+        downcast=...,
+    ) -> Series | None:
+        ...
+
     @doc(NDFrame.fillna, **_shared_doc_kwargs)
     def fillna(
         self,
diff --git a/pandas/core/strings/object_array.py b/pandas/core/strings/object_array.py
index f2027f2707a8b..dc4550484fa3b 100644
--- a/pandas/core/strings/object_array.py
+++ b/pandas/core/strings/object_array.py
@@ -5,7 +5,6 @@
     Pattern,
     Set,
     Union,
-    cast,
 )
 import unicodedata
 import warnings
@@ -371,9 +370,7 @@ def _str_get_dummies(self, sep="|"):
         try:
             arr = sep + arr + sep
         except TypeError:
-            arr = cast(Series, arr)
             arr = sep + arr.astype(str) + sep
-        arr = cast(Series, arr)
 
         tags: Set[str] = set()
         for ts in Series(arr).str.split(sep):