Create a new field in your layout with this calculation to return a text result, If(ContainerName = ""; "empty" )
uncheck "Do not evaluate if all referenced fields are empty"
and then you can do a search.
IsEmpty(container) is preferable, but both would work as same.
Further to this, note that empty/not empty is a classic Boolean condition. So what I would do is make the check field a number field. IsEmpty ( containerField ) will evaluate as 1 if it is true (i.e. the container field is empty) and 0 if it is false. This makes for a very quick search field—Find 1—and also a simple way to do other things, such as count the number of empty containers in the table.