code: public boolean isValidOffset(ZoneOffset offset) {
          return isGap() ? false : (getOffsetBefore().equals(offset) || getOffsetAfter().equals(offset));
      }
docs: Checks if the specified offset is valid during this transition.
  <p>
  This checks to see if the given offset will be valid at some point in the transition.
  A gap will always return false.
  An overlap will return true if the offset is either the before or after offset.
  
  @param offset  the offset to check, null returns false
  @return true if the offset is valid during the transition