Add support for MISSING in params and headers

This is an internal feature of the client class.
Entirely independently from the payload filtering process (which needs
to handle the complex payload types which may be used), a simple
helper for `dict|None` data is used to strip out MISSING from any
query params and headers before sending.

Testing also confirms the behavior of MISSING on simple JSON and
Form-POST data.

src/globus_sdk/client.py

@@ -304,8 +304,8 @@ def request(
             method=method,
             url=url,
             data=utils.PayloadWrapper._prepare(data),
-            query_params=query_params,
-            headers=rheaders,
+            query_params=utils.filter_missing(query_params),
+            headers=utils.filter_missing(rheaders),
             encoding=encoding,
             authorizer=self.authorizer,
             allow_redirects=allow_redirects,

src/globus_sdk/utils.py

@@ -57,6 +57,12 @@ def __repr__(self) -> str:
 MISSING = MissingType()
 
 
+def filter_missing(data: dict[str, t.Any] | None) -> dict[str, t.Any] | None:
+    if data is None:
+        return None
+    return {k: v for k, v in data.items() if v is not MISSING}
+
+
 def sha256_string(s: str) -> str:
     return hashlib.sha256(s.encode("utf-8")).hexdigest()
 

tests/functional/base_client/test_filter_missing.py

@@ -0,0 +1,57 @@
+import json
+import urllib.parse
+
+import pytest
+
+from globus_sdk import utils
+from globus_sdk._testing import RegisteredResponse, get_last_request, load_response
+
+
+@pytest.fixture(autouse=True)
+def setup_mock_responses():
+    load_response(
+        RegisteredResponse(
+            path="https://foo.api.globus.org/bar",
+            json={"foo": "bar"},
+        )
+    )
+    load_response(
+        RegisteredResponse(
+            path="https://foo.api.globus.org/bar",
+            method="POST",
+            json={"foo": "bar"},
+        )
+    )
+
+
+def test_query_params_can_filter_missing(client):
+    res = client.get("/bar", query_params={"foo": "bar", "baz": utils.MISSING})
+    assert res.http_status == 200
+    req = get_last_request()
+    assert req.params == {"foo": "bar"}
+
+
+def test_headers_can_filter_missing(client):
+    res = client.get("/bar", headers={"foo": "bar", "baz": utils.MISSING})
+    assert res.http_status == 200
+    req = get_last_request()
+    assert req.headers["foo"] == "bar"
+    assert "baz" not in req.headers
+
+
+def test_json_body_can_filter_missing(client):
+    res = client.post("/bar", data={"foo": "bar", "baz": utils.MISSING})
+    assert res.http_status == 200
+    req = get_last_request()
+    sent = json.loads(req.body)
+    assert sent == {"foo": "bar"}
+
+
+def test_form_body_can_filter_missing(client):
+    res = client.post(
+        "/bar", data={"foo": "bar", "baz": utils.MISSING}, encoding="form"
+    )
+    assert res.http_status == 200
+    req = get_last_request()
+    sent = urllib.parse.parse_qs(req.body)
+    assert sent == {"foo": ["bar"]}