@Override
  public String toString() {
    return portNumber + "/" + protocol;
  }
Stringifies the port with protocol, in the form {@code <port>/<protocol>}. For example: {@code
1337/TCP}.

@return the string form of the port with protocol
jib-build-plan/src/main/java/com/google/cloud/tools/jib/api/buildplan/Port.java