hi Sergio,
thanks a lot for looking into this.
i have tried several options with and without ' and this is how it responds-
1.filter=not('INDC' eq null)
error - "Literal 'null' not supported by this service."
2.filter=('INDC' ne 'null')
output has all entries , even where INDC = null or space
3.filter=(INDC ne null)
error - "Literal 'null' not supported by this service."
4.filter=not(INDC eq null)
error - "Literal 'null' not supported by this service."
so basically the only time it brings data is with syntax - ('INDC' ne 'null')