Nullable arguments

[boiche]

Description

I need to filter a query based on nullable field. Currently I cannot use the query builder to say : { neq: null } because this triggers compiler error CS0828. In order to use the null filtration properly, I've to explicitly replace all occurrences of "null" with null. It would be nice if the builder does this task for me.

[charlesdevandiere]

Fixed in #44