Avoid crashing in update_headers decorator when headers kwarg is None

Signed-off-by: Joffrey F <joffrey@docker.com>

docker/utils/decorators.py

@@ -40,7 +40,7 @@ def minimum_version(version):
 def update_headers(f):
     def inner(self, *args, **kwargs):
         if 'HttpHeaders' in self._auth_configs:
-            if 'headers' not in kwargs:
+            if not kwargs.get('headers'):
                 kwargs['headers'] = self._auth_configs['HttpHeaders']
             else:
                 kwargs['headers'].update(self._auth_configs['HttpHeaders'])

tests/unit/utils_test.py

@@ -20,9 +20,11 @@ from docker.utils import (
     create_host_config, Ulimit, LogConfig, parse_bytes, parse_env_file,
     exclude_paths, convert_volume_binds, decode_json_header, tar,
     split_command, create_ipam_config, create_ipam_pool, parse_devices,
+    update_headers,
 )
-from docker.utils.utils import create_endpoint_config
+
 from docker.utils.ports import build_port_bindings, split_port
+from docker.utils.utils import create_endpoint_config
 
 from .. import base
 from ..helpers import make_tree
@@ -34,6 +36,37 @@ TEST_CERT_DIR = os.path.join(
 )
 
 
+class DecoratorsTest(base.BaseTestCase):
+    def test_update_headers(self):
+        sample_headers = {
+            'X-Docker-Locale': 'en-US',
+        }
+
+        def f(self, headers=None):
+            return headers
+
+        client = Client()
+        client._auth_configs = {}
+
+        g = update_headers(f)
+        assert g(client, headers=None) is None
+        assert g(client, headers={}) == {}
+        assert g(client, headers={'Content-type': 'application/json'}) == {
+            'Content-type': 'application/json',
+        }
+
+        client._auth_configs = {
+            'HttpHeaders': sample_headers
+        }
+
+        assert g(client, headers=None) == sample_headers
+        assert g(client, headers={}) == sample_headers
+        assert g(client, headers={'Content-type': 'application/json'}) == {
+            'Content-type': 'application/json',
+            'X-Docker-Locale': 'en-US',
+        }
+
+
 class HostConfigTest(base.BaseTestCase):
     def test_create_host_config_no_options(self):
         config = create_host_config(version='1.19')