Standard Deviation when only one value is available

Hey,
I am trying to create a list with standard deviations.

I am using the following formula:
=IF(COUNT(B4:E4); STDEV(B4:E4);"")

4 columns are the source for the standard deviation. The formula works great, when 0 or 2 or 3 columns have values. However, when only one source value is available, then I get an error message (which is understandable).

My question is now how I can extend the formula so that Excel gives me an empty value (like it does when 0 source values are available) when only one source value is available.

Thanks
Benjamin

Great Thanks