code: public DateTime minusMinutes(int minutes) {
          if (minutes == 0) {
              return this;
          }
          long instant = getChronology().minutes().subtract(getMillis(), minutes);
          return withMillis(instant);
      }
docs: Returns a copy of this datetime minus the specified number of minutes.
  <p>
  The calculation will subtract a duration equivalent to the number of
  minutes expressed in milliseconds.
  <p>
  The following three lines are identical in effect:
  <pre>
  DateTime subtracted = dt.minusMinutes(6);
  DateTime subtracted = dt.minus(Period.minutes(6));
  DateTime subtracted = dt.withFieldAdded(DurationFieldType.minutes(), -6);
  </pre>
  <p>
  This datetime instance is immutable and unaffected by this method call.
  
  @param minutes  the amount of minutes to subtract, may be negative
  @return the new datetime minus the increased minutes
  @since 1.1