Model definition with nullable xml attribute properties

Hello,

I am trying to define a nullable property in a model definition, now when i try to test the api using the documentation on the right with an xml request type option, it fills it with a default value "string", is there any option where this attribute is not included when it is defined as a nullable field ? I mean I do'nt want it to be sent at all. if it has no value.

 

Thanks in advance!