Device.sweep_parallel does no checks on type of `params`

[thangleiter]

QumadaDevice.sweep_parallel() performs no checks on what params actually is, so as long as it's iterable something other than a sequence of parameters will lead to an obscure error down the line when the script is run.

[THuckemann]

Does this actually affect functionality or is it just about the confusing exception?

[thangleiter]

It's just about the confusing exception. One could also just check if the parsed params is empty.