8009593: [parfait] Null pointer deference in hotspot/src/share/vm/oops/constantPool.cpp

Summary: added guarantee() to print_entry_on()
Reviewed-by: kvn

src/share/vm/oops/constantPool.cpp

@@ -1852,6 +1852,7 @@ void ConstantPool::print_entry_on(const int index, outputStream* st) {
   switch (tag_at(index).value()) {
     case JVM_CONSTANT_Class :
       { Klass* k = klass_at(index, CATCH);
+        guarantee(k != NULL, "need klass");
         k->print_value_on(st);
         st->print(" {0x%lx}", (address)k);
       }