Cast to empty array

Author: dy

src/components/errorbars/index.js

@@ -19,7 +19,7 @@ errorBars.calc = require('./calc');
 
 errorBars.calcFromTrace = function(trace, layout) {
     var x = trace.x || [],
-        y = trace.y,
+        y = trace.y || [],
         len = x.length || y.length;
 
     var calcdataMock = new Array(len);