Use this parameter if you want to get the attribute name-value pairs before or after they are modified. For PUT operations, the
            possible parameter values are NONE (default) or ALL_OLD. For update operations, the possible parameter values are NONE
            (default) or ALL_OLD, UPDATED_OLD, ALL_NEW or UPDATED_NEW. 
- NONE: Nothing is returned.
- ALL_OLD: Returns the attributes of the item as they were before the operation.
- UPDATED_OLD: Returns the values of the updated attributes, only, as they were before the operation.
- ALL_NEW: Returns all the attributes and their new values after the operation.
- UPDATED_NEW: Returns the values of the updated attributes, only, as they are after the operation.
Constraints:
 Declaration Syntax
 Declaration Syntax| C# | 
public string ReturnValues { get; set; }