Add requirement for service default params (#7207)

docs/general/implementation.md

@@ -63,6 +63,8 @@ The service client will have methods that send requests to the service. These me
 
 {% include requirement/MUSTNOT id="general-params-server-validation" %} validate service parameters.  This includes null checks, empty strings, and other common validating conditions. Let the service validate any request parameters.
 
+{% include requirement/MUSTNOT id="general-params-server-defaults" %} encode default values for service parameters.  Service parameter default values can change between api-versions.  Required parameters should require a value to be passed to the client interface, and optional parameters should be elided if not specified so that the service will use default values for the requested api-version.
+
 {% include requirement/MUST id="general-params-check-devex" %} validate the developer experience when the service parameters are invalid to ensure appropriate error messages are generated by the service.  If the developer experience is compromised due to service-side error messages, work with the service team to correct prior to release.
 
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