NULL database values cause DVO seg faults

[rodney]

I've done some chip processing and I want to investigate the results with DVO. Some of the chipRuns have failed, raising the FAULT flag and leaving some fields NULL in the chipProcessedImfile table (e.g. sigma_ra and sigma_dec).

I'd like to use DVO to plot some values for those runs that succeeded (where FAULT=0):

1. clean columns

dvo: dbselect n_astrom from chipProcessedImfile where fault=0;

This works fine, because the n_astrom column has no NULL values, even where fault!=0

2. columns with NULL values

dvo: dbselect sigma_ra from chipProcessedImfile

This fails with a seg fault that ends the DVO session, b/c some of the sigma_ra values are NULL

3. columns with excluded NULL values

dvo: dbselect sigma_ra from chipProcessedImfile where fault=0;

This search should return only non-NULL values of sigma_ra, but it still fails with a seg fault.