When using "null" the WebSocket connection will fail with: "Sent non-empty 'Sec-WebSocket-Protocol' header but no response was received" so it's correct to use "undefined".
Coverage remained the same at 100.0% when pulling e797ef0b3a0bfc896f50fcf422ed715672b1645a on bennyn:patch-1 into 98ad44cbbb10caef24051823729b9323e4552d7e on pladaria:master.
When using "null" the WebSocket connection will fail with: "Sent non-empty 'Sec-WebSocket-Protocol' header but no response was received" so it's correct to use "undefined".
See: https://github.com/pladaria/reconnecting-websocket/issues/9