Behavior change of GET/SET

Due to MB-32244, operations were throwing exceptions when GET/DELETE were made against non-existent keys whereas the analogous operation on JS map calls the operation to return undefined. We must ensure that we document this behavior change resulting from the bugfix in a highlighted callout in documentation concurrently with Mad Hatter release. This must be prominently highlighted because this changes customer visible behavior, where what was an exception earlier will now return undefined value.