Content-Length header with HEAD requests?

Question

The http spec says about the HEAD request:

The HEAD method is identical to GET except that the server MUST NOT return a message-body in t

Answer 1

Contra the accepted answer, section 4.3.2 of RFC 7231 states:

The server SHOULD send the same header fields in response to a HEAD request as it would have sent if the request had been a GET, except that the payload header fields (Section 3.3)

—which is to say, Content-Length, Content-Range, Trailer, and Transfer-Encoding—

MAY be omitted.

This is even weaker than the note on SHOULD in Paul Dixon's answer:

5. MAY This word, or the adjective "OPTIONAL", mean that an item is truly optional. One vendor may choose to include the item because a particular marketplace requires it or because the vendor feels that it enhances the product while another vendor may omit the same item.

So the real answer is, you don't need to include Content-Length, but if you do, you should give the correct value.