Rule Definition
An empty catch block defeats the purpose of exceptions. When an exception occurs, nothing happens and the program fails for an unknown reason. The application can be in an unknown state that will affect subsequent processing. Since the reason for the issue (the exception type and potential embedded message) are ignored, it will require more time to fix the issue.

Remediation
The exception must be handled correctly.

Violation Code Sample

try {
   addlert("Welcome guest!");
}
catch(err) {
}

Fixed Code Sample

try {
   addlert("Welcome guest!");
}
catch(err) {
   // do something here
}

http://cwe.mitre.org/data/definitions/391.html