Index: trunk/ppMerge/src/ppMergeArguments.c
===================================================================
--- trunk/ppMerge/src/ppMergeArguments.c	(revision 21052)
+++ trunk/ppMerge/src/ppMergeArguments.c	(revision 21138)
@@ -206,5 +206,5 @@
     // Set the type of calibration frame
     const char *typeStr = psMetadataLookupStr(NULL, arguments, "-type"); // Type of calibration
-    if (strlen(typeStr) <= 0) {
+    if (!typeStr || strlen(typeStr) <= 0) {
       psError(PS_ERR_UNKNOWN, false, "No -type specified.");
       goto ERROR;