Tolerate NaNs in susie_rss shat

[karenfeng]

I encountered a corner case with susie_rss where if:

• z is not provided
• R is provided
• n is provided
• bhat is provided and completely non-missing
• shat is provided and has some missing values
• var_y is not provided

An exception is raised. However, in this case, shat is not used downstream and z is calculated and imputed with 0.

In this case, we can avoid raising any exception by providing z=bhat/shat. As a user, it would be ideal if the workaround were provided in the error message, or if an exception could be avoided altogether.

[pcarbo]

Thank you for your feedback @karenfeng. We will leave this Issue open until the problem is addressed.