Petascope - Remove automatic nillValues to translated Rasql from a WCPS query

[Bang Pham Huu]

Currently, Petascope add coverage's nillValues to translated Rasql query from a WCPS query implicitly, e.g:

for c in (test_rgb) return encode(c, "png")

with test_rgb is a 3 bands coverage with nullValues [119, 208, 248].

SELECT encode(c, "png" , "{\"metadata\":{\"resolution\":\"1\"},\"nodata\":[119.0,208.0,248.0]}") FROM test_rgb AS c

This nodata should be removed in the transated rasql query as rasdaman needs to extract it from collection's ras set type underneath.