czmq/zproc_t: `zproc_set_stdin ()` breaks everything

build.sh

#!/bin/bash
rm -f run_test
gcc -Wall -Werror -lczmq -DCZMQ_BUILD_DRAFT_API=1 zproc_issue.c -o run_test

script.sh

#!/bin/bash
  
#
# TODO
#
echo "Hello World!"

while read line
do
    sleep 1
    echo "$line"
done

zproc_issue.c

#include <czmq.h>
  
int
main ()
{
    //  Test #1: This Works 
    puts ("Test #1:");
    {
        zproc_t *proc = zproc_new ();
        assert (proc);

        zproc_set_verbose (proc, true);
        zproc_set_stdout (proc, NULL);

        zlist_t *arguments = zlist_new ();
        assert (arguments);
        zlist_append (arguments, (void *) "./script.sh");
        zproc_set_args (proc, &arguments);

        int rv = zproc_run (proc);
        assert (rv == 0);

        //  Expecting just one line 'Hello World!\n'
        zframe_t *frame = NULL;
        zsock_brecv (zproc_stdout (proc), "f", &frame);
        printf ("Received '%s'\n", (char *) zframe_data (frame));
        assert (zframe_streq (frame, "Hello World!\n"));

        zproc_kill (proc, SIGTERM);
        zclock_sleep (200);
        if (zproc_running (proc))
            zproc_kill (proc, SIGKILL);
        zclock_sleep (200);
        zproc_destroy (&proc);
    }
    puts ("Test #1: Successfull");

    //  Test #2: Just by adding stdin pipe previous example stops working
    puts ("");
    puts ("Test #2:");
    {
        zproc_t *proc = zproc_new ();
        assert (proc);

        zproc_set_verbose (proc, true);
        zproc_set_stdout (proc, NULL);
        zproc_set_stdin (proc, NULL);   //  <<<---- THIS BREAKS EVERYTHING !!!!
 
        zlist_t *arguments = zlist_new ();
        assert (arguments);
        zlist_append (arguments, (void *) "./script.sh");
        zproc_set_args (proc, &arguments);

        int rv = zproc_run (proc);
        assert (rv == 0);

        //  Expecting just one line 'Hello World!\n'
        zframe_t *frame = NULL;
        zsock_brecv (zproc_stdout (proc), "f", &frame);
        printf ("Received '%s'\n", (char *) zframe_data (frame));
        assert (zframe_streq (frame, "Hello World!\n"));

        zproc_kill (proc, SIGTERM);
        zclock_sleep (200);
        if (zproc_running (proc))
            zproc_kill (proc, SIGKILL);
        zclock_sleep (200);
        zproc_destroy (&proc);
    }
    puts ("Test #2: Successfull");

    return EXIT_SUCCESS;
}     

"zproc_issue.c" 73L, 2078C                                                                                                                                                                       19,0-1        Top