docs: public int fieldChanged(boolean bDisplayOption, int iMoveMode)
      {
          if (m_screenField == null)
              this.lookupSField();
          if (m_bChangeIfNull != null)
          {
              if ((m_bChangeIfNull.booleanValue()) && (!this.getOwner().isNull()))
                  return DBConstants.NORMAL_RETURN;
              if ((!m_bChangeIfNull.booleanValue()) && (this.getOwner().isNull()))
                  return DBConstants.NORMAL_RETURN;
          }
          if (m_screenField != null)
              m_screenField.requestFocus();
          return DBConstants.NORMAL_RETURN;
      }