If property-name is the empty string (
"") , is the Unknown value (
?), or if the property already exists, a JsonError is raised.
 
      A CHARACTER expression representing a numeric value to which the new element is to be set. The value must match the pattern for valid JSON number values. These may be integers ([-]dddd), decimals ([-]ddd.ddd), or scientific notation ([-]ddd[.ddd]e[+|-]ddd). If 
value is the Unknown value (
?), the element is set to the a JSON null value. If the value is not a valid JSON number value or is an empty string (
""), a JsonError is raised.