diff --git a/ChangeLog.md b/ChangeLog.md
index 7de75248bb4..461208bc04e 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,14 @@
 # Change Log
 
+### 2021-02-03 - 5.6.2
+
+Autorest core version: 3.0.6318
+
+Modelerfour version: 4.15.456
+
+**Bug Fixes**
+- Bump `Modelerfour` minimum version to [correctly deal with](https://github.com/Azure/autorest.modelerfour/pull/385) parameters specified as `'required': false` in swagger  #877
+
 ### 2021-01-27 - 5.6.1
 
 Autorest core version: 3.0.6318
diff --git a/README.md b/README.md
index 20f8427b809..34cd04b3513 100644
--- a/README.md
+++ b/README.md
@@ -30,7 +30,7 @@ pass-thru:
   - subset-reducer
 version: ^3.0.6318
 use-extension:
-  "@autorest/modelerfour": 4.15.442
+  "@autorest/modelerfour": 4.15.456
 
 modelerfour:
   group-parameters: true
diff --git a/package.json b/package.json
index 767557b7c65..2f43c1de285 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
     "name": "@autorest/python",
-    "version": "5.6.1",
+    "version": "5.6.2",
     "description": "The Python extension for generators in AutoRest.",
     "scripts": {
         "prepare": "node run-python3.js prepare.py",
diff --git a/test/vanilla/Expected/AcceptanceTests/MediaTypes/mediatypes/aio/operations/_media_types_client_operations.py b/test/vanilla/Expected/AcceptanceTests/MediaTypes/mediatypes/aio/operations/_media_types_client_operations.py
index 08db3dbc8cd..e91812a88c4 100644
--- a/test/vanilla/Expected/AcceptanceTests/MediaTypes/mediatypes/aio/operations/_media_types_client_operations.py
+++ b/test/vanilla/Expected/AcceptanceTests/MediaTypes/mediatypes/aio/operations/_media_types_client_operations.py
@@ -95,7 +95,7 @@ async def analyze_body(self, input: Optional[Union[IO, "_models.SourcePath"]] =
     analyze_body.metadata = {"url": "/mediatypes/analyze"}  # type: ignore
 
     @distributed_trace_async
-    async def content_type_with_encoding(self, input: str, **kwargs) -> str:
+    async def content_type_with_encoding(self, input: Optional[str] = None, **kwargs) -> str:
         """Pass in contentType 'text/plain; encoding=UTF-8' to pass test. Value for input does not matter.
 
         :param input: Input parameter.
@@ -123,7 +123,10 @@ async def content_type_with_encoding(self, input: str, **kwargs) -> str:
         header_parameters["Accept"] = self._serialize.header("accept", accept, "str")
 
         body_content_kwargs = {}  # type: Dict[str, Any]
-        body_content = self._serialize.body(input, "str")
+        if input is not None:
+            body_content = self._serialize.body(input, "str")
+        else:
+            body_content = None
         body_content_kwargs["content"] = body_content
         request = self._client.post(url, query_parameters, header_parameters, **body_content_kwargs)
         pipeline_response = await self._client._pipeline.run(request, stream=False, **kwargs)
diff --git a/test/vanilla/Expected/AcceptanceTests/MediaTypes/mediatypes/operations/_media_types_client_operations.py b/test/vanilla/Expected/AcceptanceTests/MediaTypes/mediatypes/operations/_media_types_client_operations.py
index 1ac77f637ce..f88e612175b 100644
--- a/test/vanilla/Expected/AcceptanceTests/MediaTypes/mediatypes/operations/_media_types_client_operations.py
+++ b/test/vanilla/Expected/AcceptanceTests/MediaTypes/mediatypes/operations/_media_types_client_operations.py
@@ -106,7 +106,7 @@ def analyze_body(
     @distributed_trace
     def content_type_with_encoding(
         self,
-        input,  # type: str
+        input=None,  # type: Optional[str]
         **kwargs  # type: Any
     ):
         # type: (...) -> str
@@ -137,7 +137,10 @@ def content_type_with_encoding(
         header_parameters["Accept"] = self._serialize.header("accept", accept, "str")
 
         body_content_kwargs = {}  # type: Dict[str, Any]
-        body_content = self._serialize.body(input, "str")
+        if input is not None:
+            body_content = self._serialize.body(input, "str")
+        else:
+            body_content = None
         body_content_kwargs["content"] = body_content
         request = self._client.post(url, query_parameters, header_parameters, **body_content_kwargs)
         pipeline_response = self._client._pipeline.run(request, stream=False, **kwargs)