This patch was created by Ingo Schwarze <schwarze@usta.de>
and taken from https://marc.info/?l=mandoc-discuss&m=175200050325256&w=2

Fixes https://github.com/termux/termux-packages/issues/25261

--- a/man_validate.c	1 Jul 2025 20:06:13 -0000	1.130
+++ b/man_validate.c	8 Jul 2025 18:34:33 -0000
@@ -479,7 +479,7 @@ post_TH(CHKARGS)
 	/* ->TITLE<- MSEC DATE OS VOL */
 
 	n = n->child;
-	if (n != NULL && n->string != NULL) {
+	if (n != NULL && n->string != NULL && *n->string != '\0') {
 		for (p = n->string; *p != '\0'; p++) {
 			/* Only warn about this once... */
 			if (isalpha((unsigned char)*p) &&
@@ -492,8 +492,8 @@ post_TH(CHKARGS)
 		}
 		man->meta.title = mandoc_strdup(n->string);
 	} else {
-		man->meta.title = mandoc_strdup("");
-		mandoc_msg(MANDOCERR_TH_NOTITLE, nb->line, nb->pos, "TH");
+		man->meta.title = mandoc_strdup("UNTITLED");
+		mandoc_msg(MANDOCERR_DT_NOTITLE, nb->line, nb->pos, "TH");
 	}
 
 	/* TITLE ->MSEC<- DATE OS VOL */