Some Spanish verbs, called verbos defectivos, are conjugated only in certain persons and tenses (their remaining verbal forms do not exist as such). This is why a question may arise about whether HABER has imperative forms or not. The truth is that it does – although they are not used, since in themselves they do not possess lexical meaning, they mean nothing. That is, the imperative tense of HABER ('to have, to exist' [impersonal form]) is not used at all – I cannot command something to have/exist. We give commands to people, but not to inanimate objects. And so, here are the forms in Imperative of this verb:

HE tú
HABED Vosotros
HAYA Usted
HAYAN Ustedes