Fixed crash on OSF/1
diff --git a/trionan.c b/trionan.c
index 138d2aa..6f67c5b 100644
--- a/trionan.c
+++ b/trionan.c
@@ -324,7 +324,7 @@
   if (result == 0.0) {
     
 #if defined(TRIO_COMPILER_SUPPORTS_C99)
-    result = nan(NULL);
+    result = nan("");
 
 #elif defined(NAN) && defined(__STDC_IEC_559__)
     result = (double)NAN;