public SystemAdmin getSystemAdmin(String systemName) {
    if (!systemAdminMap.containsKey(systemName)) {
      throw new SamzaException("Cannot get systemAdmin for system " + systemName);
    }
    return systemAdminMap.get(systemName);
  }
Creates a new instance of {@link SystemAdmins} with an empty admin mapping.
@return New empty instance of {@link SystemAdmins}
samza-core/src/main/java/org/apache/samza/system/SystemAdmins.java