2.x regression "4 parameters passed where 5 expected"

This code works on 1.x, but stopped working on 2.x:

```perl
$sth->execute(
   $wf->context->param( 'account_id' ),
   $wf->context->param( 'ending_balance' ),
   $wf->context->param( 'end_date' ),
   $wf->context->param( 'recon_fx' ),
   $wf->id,
)
```

It turns out the `recon_fx` key was not defined in the context; however in 1.x, non-existing keys return `undef`. 