Returns a tentative value for oldInstance in the environment created by this stream. A persistence delegate can use its mutatesTo method to determine whether this value may be initialized to form the equivalent object at the output or whether a new object must be instantiated afresh. If the stream has not yet seen this value, null is returned.

Parameters:

oldInstance

The instance to be looked up.

Returns:  The object, null if the object has not been seen before.