Convert Gerrit account properties to Buildbot format

    Take into account missing values

def _gerrit_user_to_author(props, username="unknown"):
    """
    Convert Gerrit account properties to Buildbot format

    Take into account missing values
    """
    username = props.get("username", username)
    username = props.get("name", username)
    if "email" in props:
        username += " <%(email)s>" % props
    return username