score:3

Accepted answer

method syntax

var query = enumerable.orderby(x => x.order == null ? 1 : 0).thenby(x => x.order);

query syntax

var query = from x in enumerable
            orderby (x.order == null ? 1 : 0), x.order
            select x;

score:0

assuming order is a nullable value (not an object), you should be able to use this:

orderby null == order ? 1 : 0, order

if it is an object, you could try

orderby null == order ? 1 : 0, order.propertyname

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