code: public Observable<RoleDefinitionInner> getAsync(String scope, String roleDefinitionId) {
          return getWithServiceResponseAsync(scope, roleDefinitionId).map(new Func1<ServiceResponse<RoleDefinitionInner>, RoleDefinitionInner>() {
              @Override
              public RoleDefinitionInner call(ServiceResponse<RoleDefinitionInner> response) {
                  return response.body();
              }
          });
      }
docs: Get role definition by name (GUID).
  
  @param scope The scope of the role definition.
  @param roleDefinitionId The ID of the role definition.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the RoleDefinitionInner object