Ignore NULL headers

src/transports/http.c

@@ -213,6 +213,7 @@ static int gen_request(
 
 	if (t->owner->custom_headers) {
 		for (i = 0; i < t->owner->custom_headers->count; i++) {
+			if (t->owner->custom_headers->strings[i])
 				git_buf_printf(buf, "%s\r\n", t->owner->custom_headers->strings[i]);
 		}
 	}

src/transports/winhttp.c

@@ -412,6 +412,7 @@ static int winhttp_stream_connect(winhttp_stream *s)
 
 	if (t->owner->custom_headers) {
 		for (i = 0; i < t->owner->custom_headers->count; i++) {
+			if (t->owner->custom_headers->strings[i]) {
 				git_buf_clear(&buf);
 				git_buf_puts(&buf, t->owner->custom_headers->strings[i]);
 				if (git__utf8_to_16(ct, MAX_CONTENT_TYPE_LEN, git_buf_cstr(&buf)) < 0) {
@@ -426,6 +427,7 @@ static int winhttp_stream_connect(winhttp_stream *s)
 				}
 			}
 		}
+	}
 
 	/* If requested, disable certificate validation */
 	if (t->connection_data.use_ssl) {