Approximation "averages" doesn't return undefined

[pawelfus]

Issue

When approximating to days, line breaks in the Bollinger Bands indicator shouldn't show up.

This may not be necessary bug in the approximation method, but according to sum approx, we should return undefined:

                sum: function(arr) {
                    var len = arr.length,
                        ret;

                    // 1. it consists of nulls exclusively
                    if (!len && arr.hasNulls) {
                        ret = null;
                        // 2. it has a length and real values
                    } else if (len) {
                        ret = 0;
                        while (len--) {
                            ret += arr[len];
                        }
                    }
                    // 3. it has zero length, so just return undefined
                    // => doNothing()

                    return ret;
                },

I think docs should be updated too.

FYI @KacperMadej

Live demo with steps to reproduce

http://jsfiddle.net/nLtpemxy/1/

Workaround

http://jsfiddle.net/nLtpemxy/

Set custom approximation:

        approximation: function(top, middle, bottom) {
          var ret = [];

          Highcharts.each(arguments, function(arr) {
            ret.push(Highcharts.approximations.average(arr));
          });

          return middle.length ? ret : undefined;
        }

[lotsawa]

Thanks @pawelfus!

The workaround works well. However please notice that this problem also occurs on price envelope, and maybe other more.

Thanks again for the workaround.

[pawelfus]

Thank you for info! Resolving this issue will fix all indicators that use averages (like Bollinger bands, Price envelopes etc.).