code: public Observable<RoleAssignmentInner> getByIdAsync(String roleAssignmentId) {
          return getByIdWithServiceResponseAsync(roleAssignmentId).map(new Func1<ServiceResponse<RoleAssignmentInner>, RoleAssignmentInner>() {
              @Override
              public RoleAssignmentInner call(ServiceResponse<RoleAssignmentInner> response) {
                  return response.body();
              }
          });
      }
docs: Gets a role assignment by ID.
  
  @param roleAssignmentId The fully qualified ID of the role assignment, including the scope, resource name and resource type. Use the format, /{scope}/providers/Microsoft.Authorization/roleAssignments/{roleAssignmentName}. Example: /subscriptions/{subId}/resourcegroups/{rgname}//providers/Microsoft.Authorization/roleAssignments/{roleAssignmentName}.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the RoleAssignmentInner object