We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
KeyError: 'split_by_domain' 
```
  File "/Users/viperfx/.pyenv/versions/scrumgenius-env-3.6/lib/python3.6/site-packages/requests/sessions.py", line 581, in post
    return self.request('POST', url, data=data, json=json, **kwargs)
  File "/Users/viperfx/.pyenv/versions/scrumgenius-env-3.6/lib/python3.6/site-packages/requests/sessions.py", line 533, in request
    resp = self.send(prep, **send_kwargs)
  File "/Users/viperfx/.pyenv/versions/scrumgenius-env-3.6/lib/python3.6/site-packages/ddtrace/contrib/requests/connection.py", line 73, in _wrap_send
    span.service = _extract_service_name(instance, span, hostname=hostname)
  File "/Users/viperfx/.pyenv/versions/scrumgenius-env-3.6/lib/python3.6/site-packages/ddtrace/contrib/requests/connection.py", line 30, in _extract_service_name
    if cfg['split_by_domain'] and hostname:
KeyError: 'split_by_domain'
```

Happens on python 3.6 and 3.7

--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `ddtrace/contrib/requests/session.py`
Content:
```
1 import requests
2 
3 from ddtrace.vendor.wrapt import wrap_function_wrapper as _w
4 
5 from .connection import _wrap_send
6 
7 
8 class TracedSession(requests.Session):
9     """TracedSession is a requests' Session that is already traced.
10     You can use it if you want a finer grained control for your
11     HTTP clients.
12     """
13 
14     pass
15 
16 
17 # always patch our `TracedSession` when imported
18 _w(TracedSession, "send", _wrap_send)
19
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/ddtrace/contrib/requests/session.py b/ddtrace/contrib/requests/session.py
--- a/ddtrace/contrib/requests/session.py
+++ b/ddtrace/contrib/requests/session.py
@@ -2,6 +2,8 @@
 
 from ddtrace.vendor.wrapt import wrap_function_wrapper as _w
 
+from ddtrace import config, Pin
+
 from .connection import _wrap_send
 
 
@@ -16,3 +18,4 @@
 
 # always patch our `TracedSession` when imported
 _w(TracedSession, "send", _wrap_send)
+Pin(_config=config.requests).onto(TracedSession)

{"golden_diff": "diff --git a/ddtrace/contrib/requests/session.py b/ddtrace/contrib/requests/session.py\n--- a/ddtrace/contrib/requests/session.py\n+++ b/ddtrace/contrib/requests/session.py\n@@ -2,6 +2,8 @@\n \n from ddtrace.vendor.wrapt import wrap_function_wrapper as _w\n \n+from ddtrace import config, Pin\n+\n from .connection import _wrap_send\n \n \n@@ -16,3 +18,4 @@\n \n # always patch our `TracedSession` when imported\n _w(TracedSession, \"send\", _wrap_send)\n+Pin(_config=config.requests).onto(TracedSession)\n", "issue": "KeyError: 'split_by_domain' \n```\r\n  File \"/Users/viperfx/.pyenv/versions/scrumgenius-env-3.6/lib/python3.6/site-packages/requests/sessions.py\", line 581, in post\r\n    return self.request('POST', url, data=data, json=json, **kwargs)\r\n  File \"/Users/viperfx/.pyenv/versions/scrumgenius-env-3.6/lib/python3.6/site-packages/requests/sessions.py\", line 533, in request\r\n    resp = self.send(prep, **send_kwargs)\r\n  File \"/Users/viperfx/.pyenv/versions/scrumgenius-env-3.6/lib/python3.6/site-packages/ddtrace/contrib/requests/connection.py\", line 73, in _wrap_send\r\n    span.service = _extract_service_name(instance, span, hostname=hostname)\r\n  File \"/Users/viperfx/.pyenv/versions/scrumgenius-env-3.6/lib/python3.6/site-packages/ddtrace/contrib/requests/connection.py\", line 30, in _extract_service_name\r\n    if cfg['split_by_domain'] and hostname:\r\nKeyError: 'split_by_domain'\r\n```\r\n\r\nHappens on python 3.6 and 3.7\n", "before_files": [{"content": "import requests\n\nfrom ddtrace.vendor.wrapt import wrap_function_wrapper as _w\n\nfrom .connection import _wrap_send\n\n\nclass TracedSession(requests.Session):\n    \"\"\"TracedSession is a requests' Session that is already traced.\n    You can use it if you want a finer grained control for your\n    HTTP clients.\n    \"\"\"\n\n    pass\n\n\n# always patch our `TracedSession` when imported\n_w(TracedSession, \"send\", _wrap_send)\n", "path": "ddtrace/contrib/requests/session.py"}], "after_files": [{"content": "import requests\n\nfrom ddtrace.vendor.wrapt import wrap_function_wrapper as _w\n\nfrom ddtrace import config, Pin\n\nfrom .connection import _wrap_send\n\n\nclass TracedSession(requests.Session):\n    \"\"\"TracedSession is a requests' Session that is already traced.\n    You can use it if you want a finer grained control for your\n    HTTP clients.\n    \"\"\"\n\n    pass\n\n\n# always patch our `TracedSession` when imported\n_w(TracedSession, \"send\", _wrap_send)\nPin(_config=config.requests).onto(TracedSession)\n", "path": "ddtrace/contrib/requests/session.py"}]}