Index: generic/gentclAPI.tcl
===================================================================
diff -u -N -r0e247f618346f3d25ffe2c30633bf75bc1f67055 -rec070e95f0d54ebae32e27b9a3251d7ec05d39ad
--- generic/gentclAPI.tcl	(.../gentclAPI.tcl)	(revision 0e247f618346f3d25ffe2c30633bf75bc1f67055)
+++ generic/gentclAPI.tcl	(.../gentclAPI.tcl)	(revision ec070e95f0d54ebae32e27b9a3251d7ec05d39ad)
@@ -156,7 +156,8 @@
       set argNum 3
       append intro \
           "  NsfClass *cl =  NsfObjectToClass(clientData);" \n\n \
-          "  assert(objc > 0);" \n
+          "  assert(objc > 0);" \n \
+          "  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, \"class\", ObjStr(objv\[0\]));"
     }
     object {
       set a  [list obj]
Index: generic/nsfAPI.h
===================================================================
diff -u -N -r0e247f618346f3d25ffe2c30633bf75bc1f67055 -rec070e95f0d54ebae32e27b9a3251d7ec05d39ad
--- generic/nsfAPI.h	(.../nsfAPI.h)	(revision 0e247f618346f3d25ffe2c30633bf75bc1f67055)
+++ generic/nsfAPI.h	(.../nsfAPI.h)	(revision ec070e95f0d54ebae32e27b9a3251d7ec05d39ad)
@@ -851,7 +851,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
     
 
       if (objc != 2) {
@@ -871,7 +871,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
   if (likely(ArgumentParse(interp, objc, objv, (NsfObject *) cl, objv[0],
                      method_definitions[NsfCCreateMethodIdx].paramDefs,
                      method_definitions[NsfCCreateMethodIdx].nrParameters, 0, NSF_ARGPARSE_BUILTIN,
@@ -893,7 +893,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
     
 
       if (objc != 2) {
@@ -913,7 +913,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
   if (likely(ArgumentParse(interp, objc, objv, (NsfObject *) cl, objv[0],
                      method_definitions[NsfCFilterGuardMethodIdx].paramDefs,
                      method_definitions[NsfCFilterGuardMethodIdx].nrParameters, 0, NSF_ARGPARSE_BUILTIN,
@@ -936,7 +936,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
     
 
       if (unlikely(objc != 1)) {
@@ -956,7 +956,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
   if (likely(ArgumentParse(interp, objc, objv, (NsfObject *) cl, objv[0],
                      method_definitions[NsfCMixinGuardMethodIdx].paramDefs,
                      method_definitions[NsfCMixinGuardMethodIdx].nrParameters, 0, NSF_ARGPARSE_BUILTIN,
@@ -980,7 +980,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
   if (likely(ArgumentParse(interp, objc, objv, (NsfObject *) cl, objv[0],
                      method_definitions[NsfCNewMethodIdx].paramDefs,
                      method_definitions[NsfCNewMethodIdx].nrParameters, 0, NSF_ARGPARSE_BUILTIN,
@@ -1003,7 +1003,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
   if (likely(ArgumentParse(interp, objc, objv, (NsfObject *) cl, objv[0],
                      method_definitions[NsfCRecreateMethodIdx].paramDefs,
                      method_definitions[NsfCRecreateMethodIdx].nrParameters, 0, NSF_ARGPARSE_BUILTIN,
@@ -1025,7 +1025,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
     
 
       if (objc < 1 || objc > 2) {
@@ -1045,7 +1045,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
   if (likely(ArgumentParse(interp, objc, objv, (NsfObject *) cl, objv[0],
                      method_definitions[NsfClassInfoFilterguardMethodIdx].paramDefs,
                      method_definitions[NsfClassInfoFilterguardMethodIdx].nrParameters, 0, NSF_ARGPARSE_BUILTIN,
@@ -1068,7 +1068,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
   if (likely(ArgumentParse(interp, objc, objv, (NsfObject *) cl, objv[0],
                      method_definitions[NsfClassInfoFiltersMethodIdx].paramDefs,
                      method_definitions[NsfClassInfoFiltersMethodIdx].nrParameters, 0, NSF_ARGPARSE_BUILTIN,
@@ -1092,7 +1092,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
   if (likely(ArgumentParse(interp, objc, objv, (NsfObject *) cl, objv[0],
                      method_definitions[NsfClassInfoForwardMethodIdx].paramDefs,
                      method_definitions[NsfClassInfoForwardMethodIdx].nrParameters, 0, NSF_ARGPARSE_BUILTIN,
@@ -1116,7 +1116,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
   if (likely(ArgumentParse(interp, objc, objv, (NsfObject *) cl, objv[0],
                      method_definitions[NsfClassInfoHeritageMethodIdx].paramDefs,
                      method_definitions[NsfClassInfoHeritageMethodIdx].nrParameters, 0, NSF_ARGPARSE_BUILTIN,
@@ -1139,7 +1139,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
   if (likely(ArgumentParse(interp, objc, objv, (NsfObject *) cl, objv[0],
                      method_definitions[NsfClassInfoInstancesMethodIdx].paramDefs,
                      method_definitions[NsfClassInfoInstancesMethodIdx].nrParameters, 0, NSF_ARGPARSE_BUILTIN,
@@ -1182,7 +1182,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
   if (likely(ArgumentParse(interp, objc, objv, (NsfObject *) cl, objv[0],
                      method_definitions[NsfClassInfoMethodMethodIdx].paramDefs,
                      method_definitions[NsfClassInfoMethodMethodIdx].nrParameters, 0, NSF_ARGPARSE_BUILTIN,
@@ -1206,7 +1206,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
   if (likely(ArgumentParse(interp, objc, objv, (NsfObject *) cl, objv[0],
                      method_definitions[NsfClassInfoMethodsMethodIdx].paramDefs,
                      method_definitions[NsfClassInfoMethodsMethodIdx].nrParameters, 0, NSF_ARGPARSE_BUILTIN,
@@ -1234,7 +1234,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
   if (likely(ArgumentParse(interp, objc, objv, (NsfObject *) cl, objv[0],
                      method_definitions[NsfClassInfoMixinOfMethodIdx].paramDefs,
                      method_definitions[NsfClassInfoMixinOfMethodIdx].nrParameters, 0, NSF_ARGPARSE_BUILTIN,
@@ -1278,7 +1278,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
   if (likely(ArgumentParse(interp, objc, objv, (NsfObject *) cl, objv[0],
                      method_definitions[NsfClassInfoMixinguardMethodIdx].paramDefs,
                      method_definitions[NsfClassInfoMixinguardMethodIdx].nrParameters, 0, NSF_ARGPARSE_BUILTIN,
@@ -1301,7 +1301,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
   if (likely(ArgumentParse(interp, objc, objv, (NsfObject *) cl, objv[0],
                      method_definitions[NsfClassInfoMixinsMethodIdx].paramDefs,
                      method_definitions[NsfClassInfoMixinsMethodIdx].nrParameters, 0, NSF_ARGPARSE_BUILTIN,
@@ -1346,7 +1346,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
   if (likely(ArgumentParse(interp, objc, objv, (NsfObject *) cl, objv[0],
                      method_definitions[NsfClassInfoSlotobjectsMethodIdx].paramDefs,
                      method_definitions[NsfClassInfoSlotobjectsMethodIdx].nrParameters, 0, NSF_ARGPARSE_BUILTIN,
@@ -1372,7 +1372,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
   if (likely(ArgumentParse(interp, objc, objv, (NsfObject *) cl, objv[0],
                      method_definitions[NsfClassInfoSubclassMethodIdx].paramDefs,
                      method_definitions[NsfClassInfoSubclassMethodIdx].nrParameters, 0, NSF_ARGPARSE_BUILTIN,
@@ -1416,7 +1416,7 @@
 
   assert(clientData != NULL);
   assert(objc > 0);
-
+  if (unlikely(cl == NULL)) return NsfDispatchClientDataError(interp, clientData, "class", ObjStr(objv[0]));
   if (likely(ArgumentParse(interp, objc, objv, (NsfObject *) cl, objv[0],
                      method_definitions[NsfClassInfoSuperclassMethodIdx].paramDefs,
                      method_definitions[NsfClassInfoSuperclassMethodIdx].nrParameters, 0, NSF_ARGPARSE_BUILTIN,