I want to construct an optional keyword search, only if the keyword field is populated.

I want to search in the field CATALOG_DESC.
This is what I have under the field as criteria in the query, it won't work.

IIf([Forms]![Form Shelf Life]![Keyword],"*[Forms]![Form Shelf Life]![keyword]*",[CATALOG_DESC])

The true condition doesn't work.
Basically, I'm trying to say if true set criteria: *keyword*

Help anyone???