code: public Observable<ServiceResponse<RoleAssignmentInner>> createWithServiceResponseAsync(String scope, String roleAssignmentName, RoleAssignmentCreateParameters parameters) {
          if (scope == null) {
              throw new IllegalArgumentException("Parameter scope is required and cannot be null.");
          }
          if (roleAssignmentName == null) {
              throw new IllegalArgumentException("Parameter roleAssignmentName is required and cannot be null.");
          }
          if (parameters == null) {
              throw new IllegalArgumentException("Parameter parameters is required and cannot be null.");
          }
          Validator.validate(parameters);
          final String apiVersion = "2018-09-01-preview";
          return service.create(scope, roleAssignmentName, parameters, apiVersion, this.client.acceptLanguage(), this.client.userAgent())
              .flatMap(new Func1<Response<ResponseBody>, Observable<ServiceResponse<RoleAssignmentInner>>>() {
                  @Override
                  public Observable<ServiceResponse<RoleAssignmentInner>> call(Response<ResponseBody> response) {
                      try {
                          ServiceResponse<RoleAssignmentInner> clientResponse = createDelegate(response);
                          return Observable.just(clientResponse);
                      } catch (Throwable t) {
                          return Observable.error(t);
                      }
                  }
              });
      }
docs: Creates a role assignment.
  
  @param scope The scope of the role assignment to create. The scope can be any REST resource instance. For example, use '/subscriptions/{subscription-id}/' for a subscription, '/subscriptions/{subscription-id}/resourceGroups/{resource-group-name}' for a resource group, and '/subscriptions/{subscription-id}/resourceGroups/{resource-group-name}/providers/{resource-provider}/{resource-type}/{resource-name}' for a resource.
  @param roleAssignmentName The name of the role assignment to create. It can be any valid GUID.
  @param parameters Parameters for the role assignment.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the RoleAssignmentInner object