Hi Josh,
I'm trying to import a numeric double. I think NULL is only for objects? Blank numeric values are NA in my data frame. I am able to get the import to work with NA values is to specify the column as text(string) in the List design, but I'm afraid of losing some precision and don't want to have to convert a character to numeric for any subsequent analysis on these results. The numeric values i'm trying to import are pvalues and CV. If I convert the NAs to a standard but nonsensical value like 9999999999, then it will import ok. For now, I'm using this workaround unless you happen to know a better way to get around it.