getAndPut abstract method
Associates the specified value with the specified key in this stash,
and returns any existing value. If the stash previously contained
a mapping for the key, the old value is replaced by the specified value
key: key with which the specified value is to be associatedvalue: value to be associated with the specified key
The previous value is returned, or null if there was no value
associated with the key previously.
Implementation
Future<T?> getAndPut(String key, T value);