Missing Field handling error

[ThePorge]

I get data files that sometimes have and ID. If this ID exists it will be what I need to use. However if no ID is in the data file it won't even have the field for the ID data. I then have to generate an ID based on the input file name. Is there a way to handle a field name not being present in the data file without throwing an error?
I get these data files all the time and I have to link up to the new file and output a pdf. Right now it looks like the only solution is to put the field name in the data, but that's a hassle with the frequency of doing this.