Function is_null 

pub fn is_null<'a, V, E>(
    expr: E,
) -> SQLExpr<'a, V, <V::DialectMarker as DialectTypes>::Bool, NonNull, E::Aggregate>
where
    V: SQLParam + 'a,
    E: Expr<'a, V>,

IS NULL check.

Returns a boolean expression checking if the value is NULL. Any expression type can be null-checked.