IsNullable не может быть присвоено значение "false" для типа Nullable<<var>X</var>>. Попробуйте использовать тип "<var>X</var>" или удалите свойство IsNullable из атрибута <var>Y</var>.

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IsNullable may not be set to 'false' for a Nullable<<var>X</var>> type. Consider using '<var>X</var>' type or removing the IsNullable property from the <var>Y</var> attribute.

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