return command - exit (or return known value) if no results found

I have a search that is basically (there are actually 2 sub searches, but this makes it easier to understand):

index="weblogs" [ SEARCH index="custcomplaintlogs" earliest=-1d | return 50 $custsession ]

This normally returns the weblogs that contain any of the customer sessions where the customers complained (ie: find what the complaining customer actually did on the site). However when there are no results in "custcomplaintlogs" over the last day it returns EVERYTHING from "weblogs". If there is something in "custcomplaintlogs" it will give the weblogs for the customers session only.

How can I stop it returning everything if the subsearch has no results. I want to either exit, or return something that will match nothing in the weblogs.