get_string_member_with_default
Description:
[ Version ( since = "1.6" ) ]
public unowned string get_string_member_with_default (string member_name, string default_value)
  public unowned string get_string_member_with_default (string member_name, string default_value)
Convenience function that retrieves the string value stored in member_name of this.
If member_name does not exist, does not contain a scalar value, or contains `null`, then default_value is returned 
      instead.
Parameters:
| this | 
           a JSON object  | 
      
| member_name | 
           the name of the this member  | 
      
| default_value | 
           the value to return if   | 
      
Returns:
| 
           the string value of the object's member, or the given default  |