code: public CMARole fetchOne(String spaceId, String roleId) {
      assertNotNull(spaceId, "spaceId");
      assertNotNull(roleId, "roleId");
  
      return service.fetchOne(spaceId, roleId).blockingFirst();
    }
docs: Fetches one role by its id from Contentful.
  <p>
  This method will override the configuration specified through
  {@link CMAClient.Builder#setSpaceId(String)} and will ignore
  {@link CMAClient.Builder#setEnvironmentId(String)}.
  
  @param spaceId the space this role is hosted by.
  @param roleId  the id of the role to be found.
  @return null if no role was found, otherwise the found role.
  @throws IllegalArgumentException if space id is null.
  @throws IllegalArgumentException if role id is null.