Empty Content-Type in curl_easy_perform GET request - libcurl

Question

Kindly disregard this issue, the problems seems to lie in werkzeug.
I believe I have detected a problem with Content-Type for GET requests sent using curl_easy_perform, in libcurl version 7.29 (CentOS 7).
The problem is that the HTTP header Content-Type is present (with empty value) in the request:
Content-Type:
In Ubuntu 18.04, with libcurl 7.58, this problem doesn't occur (as expected the header is not present in the request). I've searched Changlogs but without finding anything about this assumed fix. I did find some mention of the very same bug fixed in the PHP-curl library.
So, my question is simply: is it true that this behaviour has been fixed somewhere between 7.29 and 7.58 ?
I just made a test implementation, as short as possible, to see the problem.
This is the entire code:
#include <stdio.h> // fprintf, ...
#include <stdlib.h> // exit
#include <curl/curl.h> // curl
#include <curl/curlver.h> // VERSION
int main(int argC, char* argV[])
{
CURL* curlP;
CURLcode cc;
printf("curl version: %s\n", LIBCURL_VERSION);
curlP = curl_easy_init();
if (curlP == NULL)
{
fprintf(stderr, "curl_easy_init failed: %s\n", curl_easy_strerror(cc));
exit(1);
}
curl_easy_setopt(curlP, CURLOPT_URL, "localhost:1028/accumulate");
cc = curl_easy_perform(curlP);
if (cc != CURLE_OK)
{
fprintf(stderr, "curl_easy_perform() failed: %s\n", curl_easy_strerror(cc));
exit(2);
}
curl_easy_cleanup(curlP);
return 0;
}
The code is edited in a file called get.c and I compile it like this:
gcc get.c -o get -lcurl
The test runs in CentOS 7 with libcurl 7.58 (that I installed manually under /usr/local).
I have a simple test program, an accumulator, written in python, listening to port 1028, recording all requests that enters, and that spits it out on receiving a request with the URL path /dump.
Here is the entire sequence:
kz#centos7:curlTest> gcc get.c -o get -lcurl
kz#centos7:curlTest> ./get
curl version: 7.58.0
kz#centos7:curlTest> curl localhost:1028/dump
GET http://localhost:1028/accumulate
Content-Length:
Host: localhost:1028
Accept: */*
Content-Type:
=======================================
kz#centos7:curlTest>
As can be seen in this test, the GET request (sent by get to the accumulator) includes HTTP headers Content-Length and Content-Type without value.
The exact same test in Ubuntu 18.04 looks like this:
kz#xps:libcurlTest> gcc get.c -o get -lcurl
kz#xps:libcurlTest> ./get
curl version: 7.58.0
kz#xps:libcurlTest> curl localhost:1028/dump
GET http://localhost:1028/accumulate
Accept: */*
Host: localhost:1028
=======================================
kz#xps:libcurlTest>
Note the absence of Content-Lengthand Content-Type.
Before implementing this little test program, I made numerous attempts to avoid the Content-Type, by setting it in its slist to "Content-Type:", without space, with one space and with two spaces after the colon. I also tried without colon and of course without adding it to the slist (in which case it comes with the default content-type). I also tried to tell libcurl that the request is a GET, don't remember the details of that call right now.
Now, the error is probably mine, as I have very little experience using libcurl. It's just strange that all is OK in Ubuntu but not in CentOS ...