HighCharts [1] and HighStock [2] (which I use extensively on my SaaS app [3] - the home page shows a real screenshot) definitely allow gaps in the data. I can only warmly recommend both! (not affiliated with them in any way, they just do a great job).

[1] http://www.highcharts.com/demo/spline-irregular-time

[2] http://www.highcharts.com/products/highstock

[3] https://www.wisecashhq.com/