Adding assertion to make sure "type" field is always set

Author: romainbrenguier

src/util/json_expr.cpp

@@ -287,6 +287,8 @@ json_objectt json(
       std::string type_string;
       if(!lang->from_type(underlying_type, type_string, ns))
         result["type"]=json_stringt(type_string);
+      else
+        assert(false && "unknown type");
 
       mp_integer i;
       if(!to_integer(expr, i))