A character string that Oracle Rdb uses to replace retrieved null
    values. For example, you could specify a missing value of "Value
    not found" to replace null values. Specify a character string
    whose length does not exceed the length of the field. Enclose
    the string in single or double quotation marks ("string" or
    'string'). Ask for HELP on Value_expr for a complete description
    of the use of literal expressions.