Apply a {@code mapper} function on this async result.<p>
The {@code mapper} is called with the completed value and this mapper returns a value. This value will complete the result returned by this method call.<p>
When this async result is failed, the failure will be propagated to the returned async result and the {@code mapper} will not be called.
@param mapper the mapper function
@return the mapped async result
Apply a {@code mapper} function on this async result.<p>
The {@code mapper} is called with the completed value and this mapper returns a value. This value will complete the result returned by this method call.<p>
When this async result is failed, the failure will be propagated to the returned async result and the {@code mapper} will not be called.
@param mapper the mapper function @return the mapped async result