Need to check inputs in isat

[moritzpschwarz]

Hi all,

we should implement an input test and a more explicit error message for isat:

data(Nile)

test <- 0.005
isat(Nile, sis=TRUE, iis=FALSE, plot=TRUE, t.pval=test) # As expected

test <- NULL
isat(Nile, sis=TRUE, iis=FALSE, plot=TRUE, t.pval=test) # Error that is not clear where the problem comes from

test <- FALSE
isat(Nile, sis=TRUE, iis=FALSE, plot=TRUE, t.pval=test) # Weirdly enough works

test <- TRUE
isat(Nile, sis=TRUE, iis=FALSE, plot=TRUE, t.pval=test) # Error that is not clear where the problem comes from

Especially why the third one works is weird.
I think we need to use eval() again but there must be a better way...