Detect null slot pointer instead of crashing.
Detect null slot pointer instead of crashing.

ekr/nss-old,nmav/nss,ekr/nss-old,ekr/nss-old,ekr/nss-old,ekr/nss-old,ekr/nss-old,nmav/nss,nmav/nss,nmav/nss,ekr/nss-old,nmav/nss,nmav/nss,nmav/nss