Index: tol/btol/bgrammar/graimp.cpp
===================================================================
--- tol/btol/bgrammar/graimp.cpp	(revision aaf052850b545c868abc4d245cffcf6209cde26d)
+++ tol/btol/bgrammar/graimp.cpp	(revision 258606d55ad48d65a40f80f9f9058f37e6ccedb9)
@@ -160,4 +160,9 @@
 //--------------------------------------------------------------------
 {
+  if(!g)
+  {
+    Error("[TknFindOperand] Null grammar not allowed !");
+    return(NULL);
+  }
 #ifdef TRACE_LEVEL
   BText fun = BText("TknFindOperand(")+g->Name()+","+tok->Name();
@@ -231,4 +236,9 @@
 //--------------------------------------------------------------------
 {
+  if(!g)
+  {
+    Error("[TknFindOperator] Null grammar not allowed !");
+    return(NULL);
+  }
 #ifdef TRACE_LEVEL
   BText fun = BText("TknFindOperator(")+g->Name()+","+tok->Name()+")";
@@ -795,5 +805,6 @@
     }
     // find BINARY in Grammar of first_arg.
-    BOperator * ope = TknFindOperator(f_gra,tok,error);
+    BOperator * ope = NULL;
+    if(f_gra) { ope = TknFindOperator(f_gra,tok,error); }
     if (ope) { result = ope->Evaluate(args); }
   }