inconsistence when comparing element reference with null value constant

[Dimitar Misev]

Queries illustrating the issue:

rasql -q 'create type FloatSetNulls as set (FloatImage null values [-999])'
rasql -q 'create collection test FloatSetNulls'
rasql -q 'insert into test values <[0:0,0:1] 1f, -999f>'

# 1
rasql -q 'select c[0,0] != -999 from test as c' --out string | grep Result
  Result element 1: f
# 2
rasql -q 'select c[0,1] != -999 from test as c' --out string | grep Result
  Result element 1: f
# 3
rasql -q 'select c[0,0] = -999 from test as c' --out string | grep Result
  Result element 1: f
# 4
rasql -q 'select c[0,1] = -999 from test as c' --out string | grep Result
  Result element 1: t

#1 should return t as well. Maybe the = operator is handled with null values in mind, but not !=?