public SystemAdmin getSystemAdmin(String systemName, String adminLabel) {
    if (systemAdminMap.containsKey(systemName) && systemAdminMap.get(systemName).isStopped()) {
      systemAdminMap.clear();
    }
    return getSystemAdmins(adminLabel).get(systemName);
  }
Get {@link SystemAdmin} instance for given system name.

@param systemName System name
@return SystemAdmin of the system if it exists, otherwise null.
samza-core/src/main/java/org/apache/samza/config/SystemConfig.java