Kelli left a very high paying job to join Stephen's accounting firm based on Stephen's promise to give her a job if she would come to his firm. After Kelli quits her job and relocates to live near Stephen's firm, he tells her he was joking and really did not want to give her the job. If Kelli sues Stephen, which doctrine may a court use to prevent Stephen from revoking his offer?

The statute of frauds

Commercial impracticability

Breach of contract

Promissory estoppel