[FIX] display 'undefined' in case of falsy graph value rather than empty label

bzr revid: xmo@openerp.com-20130610071151-15lhz4o95tl4clak

diff --cc addons/web_graph/static/src/js/graph.js
index 55ce776,28e1cf6..a84bb53
--- 1/addons/web_graph/static/src/js/graph.js
--- 2/addons/web_graph/static/src/js/graph.js
+++ b/addons/web_graph/static/src/js/graph.js
@@@ -365,10 -366,10 +366,10 @@@ instance.web_graph.GraphView = instance
          }).then(function() {
              var res = {
                  'data': result,
-                 'ticks': _.map(ticks, function(el, key) { return [el, key] })
+                 'ticks': _.map(ticks, function(el, key) { return [el, key || _t("Undefined")] })
              };
              return res;
 -        });
 +        }));
      },
  
      // Render the graph and update menu styles