Gets the offset applicable at the specified instant _in these rules.
!(p)
The mapping from an instant to an offset is simple, there is only
one valid offset for each instant.
This method returns that offset.
@param instant the instant to find the offset for, not null, but null
may be ignored if the rules have a single offset for all instants
@return the offset, not null
Gets the offset applicable at the specified instant _in these rules. !(p) The mapping from an instant to an offset is simple, there is only one valid offset for each instant. This method returns that offset.
@param instant the instant to find the offset for, not null, but null may be ignored if the rules have a single offset for all instants @return the offset, not null