def convert_boot_type (boot_type):
    """
    Convert a next boot type parameter to the string that needs to be passed to system functions.
    
    :param boot_type: The boot type parameter passed to the command.  If this is None, no conversion
    is performed.
    
    :return The string identifier for the boot type.  This will be empty if the boot type is not
    valid.
    """
    
    if (boot_type is not None):
        if ((boot_type == "1") or (boot_type == "nooverride")):
            boot_type = "none"
        elif ((boot_type == "2") or (boot_type == "forcepxe")):
            boot_type = "pxe"
        elif ((boot_type == "3") or (boot_type == "forcedefaulthdd")):
            boot_type = "disk"
        elif ((boot_type == "4") or (boot_type == "forceintobiossetup")):
            boot_type = "bios"
        elif ((boot_type == "5") or (boot_type == "forcefloppyorremovable")):
            boot_type = "floppy"
        else:
            boot_type = ""
            
    return boot_type