whereIfNotNull<V> method
Adds predicate only when value is not null.
The callback is not invoked for null, so whereIfNotNull(id, …) is
safe in a search form where an empty box means "no filter".
Implementation
S whereIfNotNull<V>(
V? value,
MssqlCondition Function(TFields fields, V value) predicate,
) {
if (value == null) return _self;
return where((f) => predicate(f, value));
}