JS error when changing interval time

[manumura]

With default config, I can see 3 buttons to switch interval time : 1M 5M 15M.
I got a JS error in the console when clicking one of these buttons, for example when clicking on 5M :

Uncaught TypeError: Cannot read property '1' of null at Socket.<anonymous> (status:397) at Socket.Emitter.emit (socket.io.min.js:3) at Socket.onevent (socket.io.min.js:3) at Socket.onpacket (socket.io.min.js:3) at Manager.<anonymous> (socket.io.min.js:3) at Manager.Emitter.emit (socket.io.min.js:3) at Manager.ondecoded (socket.io.min.js:2) at Decoder.<anonymous> (socket.io.min.js:3) at Decoder.Emitter.emit (socket.io.min.js:2) at Decoder.add (socket.io.min.js:3)

When clicking on 1M, error is : Cannot read property '1' of null.

The graphs are messed up after the error happens.
Thanks for your help !