code: public static Minutes minutesIn(ReadableInterval interval) {
          if (interval == null)   {
              return Minutes.ZERO;
          }
          int amount = BaseSingleFieldPeriod.between(interval.getStart(), interval.getEnd(), DurationFieldType.minutes());
          return Minutes.minutes(amount);
      }
docs: Creates a <code>Minutes</code> representing the number of whole minutes
  in the specified interval.
  
  @param interval  the interval to extract minutes from, null returns zero
  @return the period in minutes
  @throws IllegalArgumentException if the partials are null or invalid