Seems like specifically looking for the value None would be both more…

… explicit and more accurate with respect to the documentation.

boto/gs/resumable_upload_handler.py

@@ -512,7 +512,7 @@ def send_file(self, key, fp, headers, cb=None, num_cb=10):
         # This is gsutil's way of asking boto to refrain from auto-generating
         # that header.
         CT = 'Content-Type'
-        if CT in headers and not headers[CT]:
+        if CT in headers and headers[CT] is None:
           del headers[CT]
 
         fp.seek(0, os.SEEK_END)

boto/s3/key.py

@@ -573,11 +573,11 @@ def sender(http_conn, method, path, data, headers):
             # header and depend on the receiving server to set the content
             # type. This can be achieved by setting headers['Content-Type'] 
             # to None when calling this method.
-            if headers['Content-Type']:
-                self.content_type = headers['Content-Type']
-            else:
+            if headers['Content-Type'] is None:
                 # Delete null Content-Type value to skip sending that header.
                 del headers['Content-Type']
+            else:
+                self.content_type = headers['Content-Type']
         elif self.path:
             self.content_type = mimetypes.guess_type(self.path)[0]
             if self.content_type == None: