diff --git a/integration_tests/web/test_issue_670.py b/integration_tests/web/test_issue_670.py
new file mode 100644
index 000000000..3fe0d827d
--- /dev/null
+++ b/integration_tests/web/test_issue_670.py
@@ -0,0 +1,50 @@
+import asyncio
+import io
+import logging
+import os
+import unittest
+
+from integration_tests.env_variable_names import SLACK_SDK_TEST_BOT_TOKEN
+from integration_tests.helpers import async_test
+from slack import WebClient
+
+
+class TestWebClient(unittest.TestCase):
+    """Runs integration tests with real Slack API
+
+    https://github.com/slackapi/python-slackclient/issues/670
+    """
+
+    def setUp(self):
+        self.logger = logging.getLogger(__name__)
+        self.bot_token = os.environ[SLACK_SDK_TEST_BOT_TOKEN]
+        self.sync_client: WebClient = WebClient(token=self.bot_token, run_async=False, loop=asyncio.new_event_loop())
+        self.async_client: WebClient = WebClient(token=self.bot_token, run_async=True)
+
+    def tearDown(self):
+        pass
+
+    def test_issue_670(self):
+        client = self.sync_client
+        buff = io.BytesIO(b'here is my data but not sure what is wrong.......')
+        buff.seek(0)
+        upload = client.files_upload(
+            file=buff,
+            filename="output.text",
+            filetype="text",
+            title=None,
+        )
+        self.assertIsNotNone(upload)
+
+    @async_test
+    async def test_issue_670_async(self):
+        client = self.async_client
+        buff = io.BytesIO(b'here is my data but not sure what is wrong.......')
+        buff.seek(0)
+        upload = await client.files_upload(
+            file=buff,
+            filename="output.text",
+            filetype="text",
+            title=None,
+        )
+        self.assertIsNotNone(upload)
diff --git a/slack/web/base_client.py b/slack/web/base_client.py
index 748407951..3ef78f42d 100644
--- a/slack/web/base_client.py
+++ b/slack/web/base_client.py
@@ -149,6 +149,13 @@ def api_call(
         if auth:
             auth = BasicAuth(auth["client_id"], auth["client_secret"])
 
+        if data:
+            data = {k: v for k, v in data.items() if v is not None}
+        if files:
+            files = {k: v for k, v in files.items() if v is not None}
+        if params:
+            params = {k: v for k, v in params.items() if v is not None}
+
         req_args = {
             "headers": self._get_headers(has_json, has_files, headers),
             "data": data,