CriteriaValue  - преобразование (CriteriaValue to NullableInt64)

public static implicit operator long? (
	CriteriaValue value
)

Public Shared Widening Operator CType ( 
	value As CriteriaValue
) As Long?

static implicit operator Nullable<long long> (
	CriteriaValue^ value
)

F# не поддерживает объявление новых операторов приведения.