Shadow property has no effect in solidgauge

[kamilkulig]

Expected behaviour

Some sort of shadow should appear or these options shouldn't be available in the API:

• https://api.highcharts.com/highcharts/series.solidgauge.shadow
• https://api.highcharts.com/highcharts/plotOptions.solidgauge.shadow

Actual behaviour

There's no any shadow.

Live demo

Shadow configured via object: http://jsfiddle.net/kkulig/dL2ezor5/
true flag for enabling the shadow: http://jsfiddle.net/kkulig/7ueja69c/