Clarify $select behavior for properties of "null" instances

Change to Each select item in the $select clause indicates that the response MUST include the declared or dynamic properties, actions and functions identified by that select item. If a select item is a path expression requesting a component of an entity or complex property and the entity or complex property is null on an instance, then the entity or complex property is included and represented as null . That is pull up the last sentence of the section right after the first sentence in this issue.