You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: write.go
    path of file: ./repos/scan4all/vendor/golang.org/x/crypto/openpgp
    
    the code of the file until where you have to start completion: // Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in 
    
func Sign(output io.Writer, signed *Entity, hints *FileHints, config *packet.Config) (input io.WriteCloser, err error) {
	if signed == nil {
		return nil, errors.InvalidArgumentError("no signer provided")
	}

	// These are the possible hash functions that we'll use for the signature.
	candidateHashes := []uint8{
		hashToHashId(crypto.SHA256),
		hashToHashId(crypto.SHA384),
		hashToHashId(crypto.SHA512),
		hashToHashId(crypto.SHA1),
		hashToHashId(crypto.RIPEMD160),
	}
	defaultHashes := candidateHashes[len(candidateHashes)-1:]
	preferredHashes := signed.primaryIdentity().SelfSignature.PreferredHash
	if len(preferredHashes) == 0 {
		preferredHashes = defaultHashes
	}
	candidateHashes = intersectPreferences(candidateHashes, preferredHashes)
	return writeAndSign(noOpCloser{output}, candidateHashes, signed, hints, config)
}