code: @Override
      public boolean isSupported(TemporalUnit unit) {
          if (unit instanceof ChronoUnit) {
              return unit == MONTHS || unit == YEARS || unit == DECADES || unit == CENTURIES || unit == MILLENNIA || unit == ERAS;
          }
          return unit != null && unit.isSupportedBy(this);
      }
docs: Checks if the specified unit is supported.
  <p>
  This checks if the specified unit can be added to, or subtracted from, this year-month.
  If false, then calling the {@link #plus(long, TemporalUnit)} and
  {@link #minus(long, TemporalUnit) minus} methods will throw an exception.
  <p>
  If the unit is a {@link ChronoUnit} then the query is implemented here.
  The supported units are:
  <ul>
  <li>{@code MONTHS}
  <li>{@code YEARS}
  <li>{@code DECADES}
  <li>{@code CENTURIES}
  <li>{@code MILLENNIA}
  <li>{@code ERAS}
  </ul>
  All other {@code ChronoUnit} instances will return false.
  <p>
  If the unit is not a {@code ChronoUnit}, then the result of this method
  is obtained by invoking {@code TemporalUnit.isSupportedBy(Temporal)}
  passing {@code this} as the argument.
  Whether the unit is supported is determined by the unit.
  
  @param unit  the unit to check, null returns false
  @return true if the unit can be added/subtracted, false if not