Format date/time as duration

If we have a #duration in Power Query M and then try to manipulate it in DAX it will be converted to a date/time. Now if you still want to have the date/time displayed like a #duration you can use the following:

VAR DurationAsDecimal = [#duration]
RETURN
IF(ISBLANK(DurationAsDecimal), BLANK(),
    IF(TRUNC(DurationAsDecimal)<>INT(DurationAsDecimal),
        "-"&TRUNC(DurationAsDecimal)&"."&FORMAT(DurationAsDecimal,"HH:mm:ss"),
        INT(DurationAsDecimal)&"."&FORMAT(DurationAsDecimal,"HH:mm:ss")
    )
)