docs: public String getSQLFilter(String strSeekSign, String strCompare, boolean bComparison) 
      {
          String strValue = null;
          String strSign = strSeekSign;
          if ((strSign == null) || (strSign.equals("==")))
              strSign = "=";
          FieldInfo field = this.getField();
          boolean bIsNull = true;
          if (field != null) if (!field.isNull())
              bIsNull = false;
          if (strCompare != null)
          {
              strValue = strCompare;
              bIsNull = false;
          }
          if (bIsNull)
              if (bComparison)
                  if ((!DBConstants.EQUALS.equals(strSign)) && (!FileListener.NOT_EQUAL.equals(strSign)))
                      bIsNull = false;        // If comparison is not not =, and value is null, must do <= '' or <= 0
          if (bIsNull == false)
          {
              if (strValue == null)
                  strValue = this.getSQLString();
              if (!strValue.equals("?"))
                  strValue = BaseField.addQuotes(strValue, this.getSQLQuote(true), this.getSQLQuote(false));  // Don't do this! Override and add quotes!
          }
          else
          { // Special logic to handle nulls
              if (bComparison)
              {
                  if (FileListener.NOT_EQUAL.equals(strSign))
                      strSign = " IS NOT";
                  else
                      strSign = " IS";
              }
              strValue = " NULL";
          }
          String strFilter = strSign + strValue;
          return strFilter;
      }