Normally, there is no way for the NDF_ system to know what values have been
assigned to an array component, so responsibility for setting the
bad-pixel flag rests entirely with the application.
One exception to this occurs, however, if an initialisation option of
`/ZERO' is used and results in an array full of zeros being mapped (see
§).
In this case, the bad-pixel flag will be set to .FALSE. reflecting the
resulting absence of bad pixels.