double precision IS NULL does not work ?

Hello

I have those DOUBLE PRECISION fields, sometimes containing null values:

sql>select count(1), range_low from omop.measurement group by range_low; +-----------+--------------------------+ | L2 | range_low | +===========+==========================+ | 304875924 | null | | 9448250 | 50 | | 16519843 | 0 | | 13198932 | 10 | | 14364002 | 20 | | 3964808 | 30 | | 2998528 | 3 | | 855829 | 2 | +-----------+--------------------------+ 8 tuples

However, I am not able to filter based on is null:

sql>select count(1) from omop.measurement where range_low is null; +------+ | L3 | +======+ | 0 | +------+ 1 tuple

I am not able to understand if this behavior is normal regarding the documentation:

"The types REAL, FLOAT and DOUBLE map to the underlying implementation system. No special attention is given to the value NaN."

Thanks