Index: generic/nsfStack.c
===================================================================
diff -u -r114df8b23fa9e2e1ff71b959e42da5e0883354c4 -r22741a6333a986af0a38983a0d06580f1a0103e5
--- generic/nsfStack.c	(.../nsfStack.c)	(revision 114df8b23fa9e2e1ff71b959e42da5e0883354c4)
+++ generic/nsfStack.c	(.../nsfStack.c)	(revision 22741a6333a986af0a38983a0d06580f1a0103e5)
@@ -4,7 +4,7 @@
  *      Stack handling functions of the Next Scripting Framework.
  *
  * Copyright (C) 2010-2016 Gustaf Neumann
- * Copyright (C) 2011-2015 Stefan Sobernig
+ * Copyright (C) 2011-2016 Stefan Sobernig
  *
  * Vienna University of Economics and Business
  * Institute of Information Systems and New Media
@@ -112,9 +112,13 @@
  *
  *----------------------------------------------------------------------
  */
+void NsfShowStack(Tcl_Interp *interp) nonnull(1);
+
 void NsfShowStack(Tcl_Interp *interp) {
   Tcl_CallFrame *framePtr;
 
+  nonnull_assert(interp != NULL);
+
   fprintf(stderr, "NsfShowStack framePtr %p varFramePtr %p\n",
           (void *)Tcl_Interp_framePtr(interp), (void *)Tcl_Interp_varFramePtr(interp));
   /* framePtr = (Tcl_CallFrame *)Tcl_Interp_varFramePtr(interp);
@@ -137,8 +141,8 @@
             Tcl_CallFrame_clientData(framePtr),
             Tcl_CallFrame_level(framePtr),
             (void *)Tcl_CallFrame_nsPtr(framePtr), Tcl_CallFrame_nsPtr(framePtr)->fullName,
-            Tcl_CallFrame_objc(framePtr) && 0 ? ObjStr(Tcl_CallFrame_objv(framePtr)[0]) : "(null)",
-            Tcl_CallFrame_objc(framePtr) ? Tcl_CallFrame_objc(framePtr) : -1);
+            Tcl_CallFrame_objc(framePtr) > 0 ? ObjStr(Tcl_CallFrame_objv(framePtr)[0]) : "(null)",
+            Tcl_CallFrame_objc(framePtr) > 0 ? Tcl_CallFrame_objc(framePtr) : -1);
     if (cscPtr != NULL) {
       fprintf(stderr, " csc %p frameType %.4x flags %.6x (%s.%p %s)\n",
 	      (void *)cscPtr,
@@ -1041,7 +1045,7 @@
   { int count = 0;
     NsfClasses *unstackedEntries = RUNTIME_STATE(interp)->cscList, *nextCscPtr = unstackedEntries;
 
-    while (nextCscPtr) {
+    while (nextCscPtr != NULL) {
       NsfCallStackContent *cscPtr = (NsfCallStackContent *)nextCscPtr->cl;
       CscListRemove(interp, cscPtr, &unstackedEntries);
       CscFinish(interp, cscPtr, TCL_OK, "unwind");