public static function buildIdentityString($identities)
    {
        if (null === $identities) {
            return '';
        }

        if (is_string($identities)) {
            return $identities;
        }

        if ($identities instanceof IdentityInterface) {
            $identities = [$identities];
        }

        $stringIdentities = [];

        foreach ($identities as $identity) {
            if (null === $identity->getName()) {
                $stringIdentities[] = $identity->getEmail();
                continue;
            }

            $stringIdentities[] = sprintf('%s <%s>', $identity->getName(), $identity->getEmail());
        }

        return implode(',', $stringIdentities);
    }
public static function buildIdentityString($identities)
    {
        if (null === $identities) {
            return '';
        }

        if (is_string($identities)) {
            return $identities;
        }

        if ($identities instanceof IdentityInterface) {
            $identities = [$identities];
        }

        $stringIdentities = [];

        foreach ($identities as $identity) {
            if (null === $identity->getName()) {
                $stringIdentities[] = $identity->getEmail();
                continue;
            }

            $stringIdentities[] = sprintf('%s <%s>', $identity->getName(), $identity->getEmail());
        }

        return implode(',', $stringIdentities);
    }
@param IdentityInterface[]|IdentityInterface|string $identities

@return string