diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 167a52e5ac..aa3059dfa8 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -6,8 +6,7 @@ on:
     - 'release/*'
   pull_request:
 env:
-  CORE_REPO_SHA: f69e12fba8d0afd587dd21adbedfe751153aa73c
-
+  CORE_REPO_SHA: master
 
 jobs:
   build:
diff --git a/instrumentation/opentelemetry-instrumentation-asgi/CHANGELOG.md b/instrumentation/opentelemetry-instrumentation-asgi/CHANGELOG.md
index 686b8cf830..93399696b5 100644
--- a/instrumentation/opentelemetry-instrumentation-asgi/CHANGELOG.md
+++ b/instrumentation/opentelemetry-instrumentation-asgi/CHANGELOG.md
@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+- Return `None` for `CarrierGetter` if key not found
+  ([#1374](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/233))
+
 ## Version 0.12b0
 
 Released 2020-08-14
diff --git a/instrumentation/opentelemetry-instrumentation-asgi/src/opentelemetry/instrumentation/asgi/__init__.py b/instrumentation/opentelemetry-instrumentation-asgi/src/opentelemetry/instrumentation/asgi/__init__.py
index 1c442889a1..6391636035 100644
--- a/instrumentation/opentelemetry-instrumentation-asgi/src/opentelemetry/instrumentation/asgi/__init__.py
+++ b/instrumentation/opentelemetry-instrumentation-asgi/src/opentelemetry/instrumentation/asgi/__init__.py
@@ -34,7 +34,9 @@
 
 
 class CarrierGetter(DictGetter):
-    def get(self, carrier: dict, key: str) -> typing.List[str]:
+    def get(
+        self, carrier: dict, key: str
+    ) -> typing.Optional[typing.List[str]]:
         """Getter implementation to retrieve a HTTP header value from the ASGI
         scope.
 
@@ -43,14 +45,17 @@ def get(self, carrier: dict, key: str) -> typing.List[str]:
             key: header name in scope
         Returns:
             A list with a single string with the header value if it exists,
-             else an empty list.
+                else None.
         """
         headers = carrier.get("headers")
-        return [
+        decoded = [
             _value.decode("utf8")
             for (_key, _value) in headers
             if _key.decode("utf8") == key
         ]
+        if not decoded:
+            return None
+        return decoded
 
 
 carrier_getter = CarrierGetter()
@@ -82,11 +87,12 @@ def collect_request_attributes(scope):
     http_method = scope.get("method")
     if http_method:
         result["http.method"] = http_method
-    http_host_value = ",".join(carrier_getter.get(scope, "host"))
-    if http_host_value:
-        result["http.server_name"] = http_host_value
+
+    http_host_value_list = carrier_getter.get(scope, "host")
+    if http_host_value_list:
+        result["http.server_name"] = ",".join(http_host_value_list)
     http_user_agent = carrier_getter.get(scope, "user-agent")
-    if len(http_user_agent) > 0:
+    if http_user_agent:
         result["http.user_agent"] = http_user_agent[0]
 
     if "client" in scope and scope["client"] is not None:
diff --git a/instrumentation/opentelemetry-instrumentation-asgi/tests/test_asgi_middleware.py b/instrumentation/opentelemetry-instrumentation-asgi/tests/test_asgi_middleware.py
index cf8944ce6d..298d8ca458 100644
--- a/instrumentation/opentelemetry-instrumentation-asgi/tests/test_asgi_middleware.py
+++ b/instrumentation/opentelemetry-instrumentation-asgi/tests/test_asgi_middleware.py
@@ -164,7 +164,7 @@ def test_basic_asgi_call(self):
         outputs = self.get_all_output()
         self.validate_outputs(outputs)
 
-    def test_wsgi_not_recording(self):
+    def test_asgi_not_recording(self):
         mock_tracer = mock.Mock()
         mock_span = mock.Mock()
         mock_span.is_recording.return_value = False
@@ -312,8 +312,12 @@ def setUp(self):
 
     def test_request_attributes(self):
         self.scope["query_string"] = b"foo=bar"
+        headers = []
+        headers.append(("host".encode("utf8"), "test".encode("utf8")))
+        self.scope["headers"] = headers
 
         attrs = otel_asgi.collect_request_attributes(self.scope)
+
         self.assertDictEqual(
             attrs,
             {
@@ -324,6 +328,7 @@ def test_request_attributes(self):
                 "http.url": "http://127.0.0.1/?foo=bar",
                 "host.port": 80,
                 "http.scheme": "http",
+                "http.server_name": "test",
                 "http.flavor": "1.0",
                 "net.peer.ip": "127.0.0.1",
                 "net.peer.port": 32767,
diff --git a/instrumentation/opentelemetry-instrumentation-celery/src/opentelemetry/instrumentation/celery/__init__.py b/instrumentation/opentelemetry-instrumentation-celery/src/opentelemetry/instrumentation/celery/__init__.py
index cdf5b00618..495cbe96a1 100644
--- a/instrumentation/opentelemetry-instrumentation-celery/src/opentelemetry/instrumentation/celery/__init__.py
+++ b/instrumentation/opentelemetry-instrumentation-celery/src/opentelemetry/instrumentation/celery/__init__.py
@@ -80,7 +80,9 @@ def add(x, y):
 
 class CarrierGetter(DictGetter):
     def get(self, carrier, key):
-        value = getattr(carrier, key, [])
+        value = getattr(carrier, key, None)
+        if value is None:
+            return None
         if isinstance(value, str) or not isinstance(value, Iterable):
             value = (value,)
         return value
diff --git a/instrumentation/opentelemetry-instrumentation-celery/tests/test_getter.py b/instrumentation/opentelemetry-instrumentation-celery/tests/test_getter.py
new file mode 100644
index 0000000000..a534309750
--- /dev/null
+++ b/instrumentation/opentelemetry-instrumentation-celery/tests/test_getter.py
@@ -0,0 +1,44 @@
+# Copyright The OpenTelemetry Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from unittest import TestCase, mock
+
+from opentelemetry.instrumentation.celery import CarrierGetter
+
+
+class TestCarrierGetter(TestCase):
+    def test_get_none(self):
+        getter = CarrierGetter()
+        carrier = {}
+        val = getter.get(carrier, "test")
+        self.assertIsNone(val)
+
+    def test_get_str(self):
+        mock_obj = mock.Mock()
+        getter = CarrierGetter()
+        mock_obj.test = "val"
+        val = getter.get(mock_obj, "test")
+        self.assertEqual(val, ("val",))
+
+    def test_get_iter(self):
+        mock_obj = mock.Mock()
+        getter = CarrierGetter()
+        mock_obj.test = ["val"]
+        val = getter.get(mock_obj, "test")
+        self.assertEqual(val, ["val"])
+
+    def test_keys(self):
+        getter = CarrierGetter()
+        keys = getter.keys({})
+        self.assertEqual(keys, [])
diff --git a/instrumentation/opentelemetry-instrumentation-wsgi/CHANGELOG.md b/instrumentation/opentelemetry-instrumentation-wsgi/CHANGELOG.md
index 68bd25237c..ee3678f89e 100644
--- a/instrumentation/opentelemetry-instrumentation-wsgi/CHANGELOG.md
+++ b/instrumentation/opentelemetry-instrumentation-wsgi/CHANGELOG.md
@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+- Return `None` for `CarrierGetter` if key not found
+  ([#1374](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/233))
+
 ## Version 0.13b0
 
 Released 2020-09-17
diff --git a/instrumentation/opentelemetry-instrumentation-wsgi/src/opentelemetry/instrumentation/wsgi/__init__.py b/instrumentation/opentelemetry-instrumentation-wsgi/src/opentelemetry/instrumentation/wsgi/__init__.py
index e1ef92c6ba..b8de5c1820 100644
--- a/instrumentation/opentelemetry-instrumentation-wsgi/src/opentelemetry/instrumentation/wsgi/__init__.py
+++ b/instrumentation/opentelemetry-instrumentation-wsgi/src/opentelemetry/instrumentation/wsgi/__init__.py
@@ -68,7 +68,9 @@ def hello():
 
 
 class CarrierGetter(DictGetter):
-    def get(self, carrier: dict, key: str) -> typing.List[str]:
+    def get(
+        self, carrier: dict, key: str
+    ) -> typing.Optional[typing.List[str]]:
         """Getter implementation to retrieve a HTTP header value from the
             PEP3333-conforming WSGI environ
 
@@ -77,13 +79,13 @@ def get(self, carrier: dict, key: str) -> typing.List[str]:
             key: header name in environ object
         Returns:
             A list with a single string with the header value if it exists,
-            else an empty list.
+            else None.
         """
         environ_key = "HTTP_" + key.upper().replace("-", "_")
         value = carrier.get(environ_key)
         if value is not None:
             return [value]
-        return []
+        return None
 
     def keys(self, carrier):
         return []
diff --git a/instrumentation/opentelemetry-instrumentation-wsgi/tests/test_getter.py b/instrumentation/opentelemetry-instrumentation-wsgi/tests/test_getter.py
new file mode 100644
index 0000000000..630e5fc579
--- /dev/null
+++ b/instrumentation/opentelemetry-instrumentation-wsgi/tests/test_getter.py
@@ -0,0 +1,36 @@
+# Copyright The OpenTelemetry Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from unittest import TestCase, mock
+
+from opentelemetry.instrumentation.wsgi import CarrierGetter
+
+
+class TestCarrierGetter(TestCase):
+    def test_get_none(self):
+        getter = CarrierGetter()
+        carrier = {}
+        val = getter.get(carrier, "test")
+        self.assertIsNone(val)
+
+    def test_get_(self):
+        getter = CarrierGetter()
+        carrier = {"HTTP_TEST_KEY": "val"}
+        val = getter.get(carrier, "test-key")
+        self.assertEqual(val, ["val"])
+
+    def test_keys(self):
+        getter = CarrierGetter()
+        keys = getter.keys({})
+        self.assertEqual(keys, [])