X-Git-Url: https://git.donarmstrong.com/?a=blobdiff_plain;f=lily%2Fbreak-substitution.cc;h=3ccc16c09063bbc80beeb2b0dd8059280673ed32;hb=c730a0aab8ce3fd1785b5815122e061534e53d1c;hp=2238f4495751a7f87a3946502670258d52dbfd3e;hpb=2536405e9584f63d559653183971c0fec57ba037;p=lilypond.git

diff --git a/lily/break-substitution.cc b/lily/break-substitution.cc
index 2238f44957..3ccc16c090 100644
--- a/lily/break-substitution.cc
+++ b/lily/break-substitution.cc
@@ -478,10 +478,17 @@ substitute_mutable_property_alist (SCM alist)
       else
 	val = do_break_substitution (val);
 
-      *tail = scm_cons (scm_cons (sym, val), SCM_EOL);
-      tail = SCM_CDRLOC (*tail);
-    }
 
+      if (val != SCM_UNDEFINED)
+	{
+	  /*
+	    for ly:grob? properties, SCM_UNDEFINED could leak out
+	    through ly:grob-property
+	   */
+	  *tail = scm_cons (scm_cons (sym, val), SCM_EOL);
+	  tail = SCM_CDRLOC (*tail);
+	}
+    }
   return l;
 }