function assertNonEmpty (serverAddressesArray, serversName, routerAddress) {
  if (serverAddressesArray.length === 0) {
    throw newError(
      'Received no ' + serversName + ' from router ' + routerAddress,
      PROTOCOL_ERROR
    )
  }
}
Assert if serverAddressesArray is not empty, throws and PROTOCOL_ERROR otherwise

@param {string[]} serverAddressesArray array of addresses
@param {string} serversName the server name
@param {string} routerAddress the router address