Index: output.c
===================================================================
--- output.c.orig
+++ output.c
@@ -659,7 +659,7 @@ frame_callback (Dwfl_Frame *state, void
 
 	/* This mimics the output produced by libunwind below.  */
 	fprintf(options.output, " > %s(%s+0x%" PRIx64 ") [%" PRIx64 "]\n",
-		modname, symname, off, pc);
+		modname ?: "(null)", symname ?: "(null)", off, pc);
 
 	/* See if we can extract the source line too and print it on
 	   the next line if we can find it.  */