Filing PERM on very first job, no previous employers. Confused.

[niebula]

I got my bachelor's degree from an American university under the F-1 visa, then got sponsored for H1-B for my first job ever. My employer has decided to sponsor me for a greencard, and we have begun the PERM process. I understand you usually need reference letters from previous employers, but in my case, I have no previous employers. This is my first job ever.

How do I proceed?