Revert "add NullBehavior concept to PropertyCopier; default is to acknowledge the appropriateness of the copier while doing nothing"

This reverts commit 1bc658d8b1ef9de3367b079f080923b106fe2d5f.
add Operator.Phase
convert Hint to interface
failing test
implement optional Property
add NullBehavior concept to PropertyCopier; default is to acknowledge the appropriateness of the copier while doing nothing