--- a/modules/filters/mod_include.c
+++ b/modules/filters/mod_include.c
@@ -2729,9 +2729,15 @@
 
         /* get value */
         val_text = elts[i].val;
-        if (val_text == LAZY_VALUE)
-            val_text = add_include_vars_lazy(r, elts[i].key, ctx->time_str);
-        val_text = ap_escape_html(ctx->dpool, val_text);
+
+        if (val_text) {
+            if (val_text == LAZY_VALUE)
+                val_text = add_include_vars_lazy(r, elts[i].key, ctx->time_str);
+            val_text = ap_escape_html(ctx->dpool, val_text);
+        }
+        else {
+            val_text = ctx->intern->undefined_echo;
+        }
 
         apr_brigade_putstrs(bb, NULL, NULL, key_text, "=", val_text, "\n",
                             NULL);