Handling a missing parameter in RPG III

There are two vendor supplied programs, written in RPG III. The first
program prepares the environment for the second program.

Originally, intent was that first program would be initiated from a
menu. Now, in addition to that, it also needs to be capable of being
submitted by a scheduled job.

I can clone the first program with a new name and then modify it to
not require a display file. But, second program would also need to be
modified as it checks how it was called.

I see two possibilities here:

1) Create clone of first progra and modify second program to recognize
the validity of the second program.

2) Add a parm to the first program to indicate portions of code should
be bypassed. But, the problem as I see it, is that the existing
invocation of the first program has no provision for a parameter. If
program is called without a parameter, it will fail.

Is there a way to test for a missing parameter with RPG III?

I thought about using the LDA, but that is formatted already. Might
be possible to use it, but unknown at this point.

Any suggestions to deal with this?

John McKee