AggregateOperand does not support nested expressions and complex property paths like Max(Document.<PersonID>LastName). Only names of owned properties are supported: Max(Document).
AggregateOperand may produce null instead of zero for an empty collection on a server side.
The Single function requires that the collection contain no more than one object. If the collection contains more objects, use the Condition property to specify a condition. The collection must contain only one object that satisfies the condition; otherwise, the function's behavior is undefined (the function may return an unexpected value or throw an exception).