public void addExposedPort(Port port) {
      if (exposedPorts == null) {
        exposedPorts = new HashSet<>();
      }
      exposedPorts.add(port);
    }
Adds an exposed port entry to the container configuration.

@param port the non-null port to add
jib-core/src/main/java/com/google/cloud/tools/jib/configuration/ContainerConfiguration.java