Imputation considers only NaN; should it also consider zeros?

[acesnik]

Is your feature request related to a problem? Please describe.
I was getting some mysterious negative log2-transformed values after imputation, and it took me a while to figure out that zeros aren't being imputed. I changed them to NaN, and now they're being imputed.

Describe the solution you'd like
Adding a parameter for the preprocessing engine for which values to impute. Or change the default behavior to imputing both zeros and NaN are imputed.

Describe alternatives you've considered
I found a workaround with converting zeros to NaN before running imputation.

[JuliaS92]

We added 0 replacement with nans to the preprocessing options and only nans are imputed. This will be in the next release.