/**
* Creates a new <code>Weeks</code> by parsing a string in the ISO8601 format 'PnW'.
*
* <p>The parse will accept the full ISO syntax of PnYnMnWnDTnHnMnS however only the weeks
* component may be non-zero. If any other component is non-zero, an exception will be thrown.
*
* @param periodStr the period string, null returns zero
* @return the period in weeks
* @throws IllegalArgumentException if the string format is invalid
*/
@FromString
public static Weeks parseWeeks(String periodStr) {
if (periodStr == null) {
return Weeks.ZERO;
}
Period p = PARSER.parsePeriod(periodStr);
return Weeks.weeks(p.getWeeks());
}
