Fix lp:1302500 by evaluating an empty context to avoid error

web_context_tunnel/static/src/js/context_tunnel.js

@@ -17,6 +17,7 @@ openerp.web_context_tunnel = function(instance) {
         }
         if (!v_context) {
             v_context = (this.field || {}).context || {};
+            v_context = new instance.web.CompoundContext(v_context).set_eval_context(false);
         }
         return v_context;
     };