To conditionally report a fatal error:

Use the [Fail_If] method. Lasso will immediately halt processing of the current page or [Protect] block and report the error to the user or run any [Handle] methods that are present.

The following code will report an unknown error if the [web_request->param] named 'Required' is empty.

Note: [Action_Param] is a compatibility layer wrapper for [web_request->param]

Code

Fail_If(not string(web_request->param('Required'))->size, -1, 'Unknown Error')

Result

FAILURE: -1 Unknown Error