diff --git a/msrest/service_client.py b/msrest/service_client.py
index a204089..ac70211 100644
--- a/msrest/service_client.py
+++ b/msrest/service_client.py
@@ -138,7 +138,7 @@ class ServiceClient(object):
 
         return kwargs
 
-    def send_formdata(self, request, headers={}, content={}, **config):
+    def send_formdata(self, request, headers=None, content=None, **config):
         """Send data as a multipart form-data request.
         We only deal with file-like objects or strings at this point.
         The requests is not yet streamed.
@@ -148,11 +148,11 @@ class ServiceClient(object):
         :param dict content: Dictionary of the fields of the formdata.
         :param config: Any specific config overrides.
         """
+        if content is None:
+            content = {}
         file_data = {f: self._format_data(d) for f, d in content.items()}
-        try:
-            del headers['Content-Type']
-        except KeyError:
-            pass
+        if headers:
+            headers.pop('Content-Type', None)
         return self.send(request, headers, None, files=file_data, **config)
 
     def send(self, request, headers=None, content=None, **config):
@@ -290,7 +290,7 @@ class ServiceClient(object):
         """
         self._headers[header] = value
 
-    def get(self, url=None, params={}):
+    def get(self, url=None, params=None):
         """Create a GET request object.
 
         :param str url: The request URL.
@@ -300,7 +300,7 @@ class ServiceClient(object):
         request.method = 'GET'
         return request
 
-    def put(self, url=None, params={}):
+    def put(self, url=None, params=None):
         """Create a PUT request object.
 
         :param str url: The request URL.
@@ -310,7 +310,7 @@ class ServiceClient(object):
         request.method = 'PUT'
         return request
 
-    def post(self, url=None, params={}):
+    def post(self, url=None, params=None):
         """Create a POST request object.
 
         :param str url: The request URL.
@@ -320,7 +320,7 @@ class ServiceClient(object):
         request.method = 'POST'
         return request
 
-    def head(self, url=None, params={}):
+    def head(self, url=None, params=None):
         """Create a HEAD request object.
 
         :param str url: The request URL.
@@ -330,7 +330,7 @@ class ServiceClient(object):
         request.method = 'HEAD'
         return request
 
-    def patch(self, url=None, params={}):
+    def patch(self, url=None, params=None):
         """Create a PATCH request object.
 
         :param str url: The request URL.
@@ -340,7 +340,7 @@ class ServiceClient(object):
         request.method = 'PATCH'
         return request
 
-    def delete(self, url=None, params={}):
+    def delete(self, url=None, params=None):
         """Create a DELETE request object.
 
         :param str url: The request URL.
@@ -350,7 +350,7 @@ class ServiceClient(object):
         request.method = 'DELETE'
         return request
 
-    def merge(self, url=None, params={}):
+    def merge(self, url=None, params=None):
         """Create a MERGE request object.
 
         :param str url: The request URL.

Default argument value is mutable
Hi,

Just want to confirm, I noticed there are some methods in `ServiceClient` contain a mutable default argument, for instance: 
`def get(self, url=None, params={}):
        """Create a GET request object.

        :param str url: The request URL.
        :param dict params: Request URL parameters.
        """
        request = self._request(url, params)
        request.method = 'GET'
        return request`

And the default argument `params` is changed in`self._request(url, params)`. Is that as design? I just think it's a little wired. Thanks!

 
diff --git a/test/unittest_client.py b/test/unittest_client.py
index c22b13e..4a193ee 100644
--- a/test/unittest_client.py
+++ b/test/unittest_client.py
@@ -201,7 +201,7 @@ class TestServiceClient(unittest.TestCase):
         mock_client._format_data.return_value = "formatted"
         request = ClientRequest('GET')
         ServiceClient.send_formdata(mock_client, request)
-        mock_client.send.assert_called_with(request, {}, None, files={})
+        mock_client.send.assert_called_with(request, None, None, files={})
 
         ServiceClient.send_formdata(mock_client, request, {'id':'1234'}, {'Test':'Data'})
         mock_client.send.assert_called_with(request, {'id':'1234'}, None, files={'Test':'formatted'})

pip install -e .[dev]
parse_log_pytest
requirements.txt
pytest coverage flake8
3.5
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
attrs==22.2.0
certifi==2021.5.30
charset-normalizer==2.0.12
coverage==6.2
flake8==5.0.4
idna==3.10
importlib-metadata==4.2.0
iniconfig==1.1.1
isodate==0.6.1
mccabe==0.7.0
-e git+https://github.com/Azure/msrest-for-python.git@02b1e35c7cfb045bd4752abe800ad6912282eb6e#egg=msrest
oauthlib==3.2.2
packaging==21.3
pluggy==1.0.0
py==1.11.0
pycodestyle==2.9.1
pyflakes==2.5.0
pyparsing==3.1.4
pytest==7.0.1
requests==2.27.1
requests-oauthlib==2.0.0
six==1.17.0
tomli==1.2.3
typing_extensions==4.1.1
urllib3==1.26.20
zipp==3.6.0

name: msrest-for-python
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - ca-certificates=2025.2.25=h06a4308_0
  - certifi=2021.5.30=py36h06a4308_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.3=he6710b0_2
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - ncurses=6.4=h6a678d5_0
  - openssl=1.1.1w=h7f8727e_0
  - pip=21.2.2=py36h06a4308_0
  - python=3.6.13=h12debd9_1
  - readline=8.2=h5eee18b_0
  - setuptools=58.0.4=py36h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - wheel=0.37.1=pyhd3eb1b0_0
  - xz=5.6.4=h5eee18b_1
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - attrs==22.2.0
      - charset-normalizer==2.0.12
      - coverage==6.2
      - flake8==5.0.4
      - idna==3.10
      - importlib-metadata==4.2.0
      - iniconfig==1.1.1
      - isodate==0.6.1
      - mccabe==0.7.0
      - oauthlib==3.2.2
      - packaging==21.3
      - pluggy==1.0.0
      - py==1.11.0
      - pycodestyle==2.9.1
      - pyflakes==2.5.0
      - pyparsing==3.1.4
      - pytest==7.0.1
      - requests==2.27.1
      - requests-oauthlib==2.0.0
      - six==1.17.0
      - tomli==1.2.3
      - typing-extensions==4.1.1
      - urllib3==1.26.20
      - zipp==3.6.0
prefix: /opt/conda/envs/msrest-for-python

test/unittest_client.py::TestServiceClient::test_client_formdata_send
test/unittest_client.py::TestServiceClient::test_client_add_hook test/unittest_client.py::TestServiceClient::test_client_header test/unittest_client.py::TestServiceClient::test_client_request test/unittest_client.py::TestServiceClient::test_client_send test/unittest_client.py::TestServiceClient::test_format_data test/unittest_client.py::TestServiceClient::test_format_url
msrest/service_client.py
msrest/service_client.py